Adhesive for bonding to low surface energy surfaces

ABSTRACT

A novel polymodal asymmetric elastomeric block copolymer and a pressure sensitive adhesive, tape and adhesive backed article made therefrom, such as a polymer foam article having a substantially smooth surface prepared by melt-mixing a polymer composition and a plurality of microspheres, at least one of which is an expandable polymeric microsphere, under process conditions, including temperature and shear rate, selected to form an expandable extrudable composition; and extruding the composition through a die.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.10/203,046 filed Dec. 9, 2002 now abandoned, entitled ADHESIVE FORBONDING TO LOW SURFACE ENERGY SURFACES, which claims the benefit of PCTInternational Patent Application Serial No. PCT/US01/03463 filed Feb. 2,2001 and is a continuation-in-part of U.S. patent application Ser. No.09/496,831 filed Feb. 2, 2000, entitled ADHESIVE FOR BONDING TO LOWSURFACE ENERGY SURFACES, now U.S. Pat. No. 6,630,531 B1, the entiredisclosures of which are incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to an adhesive made from a polymodalasymmetric elastomeric block copolymer, more particularly, to such anadhesive for forming high strength bonds to low surface energy surfacesand, even more particularly, to articles made with such adhesives,including adhesive tapes.

BACKGROUND OF THE INVENTION

Block copolymers are known in the art for a variety of applicationsincluding for use in removable tape applications wherein the tape istypically removed when it is no longer needed. See, for example, U.S.Pat. Nos. 5,393,787 and 5,296,547, both of which are assigned to thepresent assignee. Such block copolymers can be formulated into apressure sensitive adhesive, which may be used to make a variety ofdifferent types of tapes including removeable tapes. Specific examplesof the various tapes which may be made include masking tapes, packagingtapes, medical tapes and autoclave indicator tapes. Additionally, thepressure sensitive adhesive may be used to make protective sheeting,labels, and facestock.

Articles incorporating a polymer foam core are known. The foam includesa polymer matrix and is characterized by a density that is lower thanthe density of the polymer matrix itself. Density reduction is achievedin a number of ways, including through creation of gas-filled voids inthe matrix (e.g., by means of a blowing agent) or inclusion of polymericmicrospheres (e.g., expandable microspheres) or non-polymericmicrospheres (e.g., glass microspheres).

SUMMARY OF THE INVENTION

The adhesives of the present invention are particularly useful forforming strong bonds to low surface energy substrates. As used herein,low surface energy substrates are those having a surface energy of lessthan about 45 dynes per centimeter, more typically less than about 40dynes per centimeter, and most typically less than about 35 dynes percentimeter.

In one aspect of the invention, a pressure sensitive adhesive isprovided that comprises 100 parts by weight of a polymodal asymmetricelastomeric block copolymer and at least one tackifier or tackifyingresin in an amount sufficient to raise the calculated Fox T_(g) of therubber phase of the adhesive to at least 245°K. The amount of tackifierused depends on the resulting T_(g), of the adhesive's rubber phase,that is obtained by the addition of the tackifier. So, more tackifiercan be added to obtain the T_(g) desired. The adhesive composition mayalso include 0 to about 50 parts by weight of a crosslinking agent and 0to about 300 parts by weight of a plasticizer. In general, thedifference between a tackifier and a plasticizer is that the addition ofa tackifier increases the T_(g) of the adhesive's rubber phase while theaddition of the plasticizer decreases the T_(g) of the adhesive's rubberphase. The polymodal asymmetric elastomeric block copolymer has theformula Q_(n) Y and comprises from about 4 to about 40 percent by weightof a polymerized monovinyl aromatic compound and from about 96 to about60 percent by weight of polymerized conjugated diene. Q represents anindividual arm of the block copolymer and has the formula S—B; nrepresents the number of arms Q in the block copolymer and is a wholenumber of at least 3; and Y is the residue of a multifunctional couplingagent. S is a nonelastomeric polymer segment endblock of a polymerizedmonovinyl aromatic homopolymer, there being at least two differentmolecular weight endblocks in the copolymer, a higher molecular weightendblock and a lower molecular weight endblock. The number averagemolecular weight of the higher molecular weight endblock (Mn)_(H) is inthe range of from about 5,000 to about 50,000. The number averagemolecular weight of the lower molecular weight endblock (Mn)_(L) is inthe range of from about 1,000 to about 10,000. The ratio(Mn)_(H)/(Mn)_(L) is at least 1.25. B is an elastomeric polymer segmentmidblock which connects each arm to the residue of a multifunctionalcoupling agent (Y) and comprises a polymerized conjugated diene orcombination of conjugated dienes.

The adhesive has a rubber phase exhibiting a calculated Fox T_(g) of atleast 245°K, and the adhesive forms a high strength bond to low surfaceenergy surfaces. As used herein, low surface energy surfaces orsubstrates exhibit a surface energy of less than 45 dyne/cm, moretypically less than 40 dyne/cm, or more typically less than 35 dyne/cm.Preferably, the rubber phase of the adhesive has a calculated Fox T_(g)of at least 250°K and, more preferably, 255°K. In addition, the rubberphase of the adhesive preferably has a calculated Fox T_(g) with anupper limit of less than 300°K and, more preferably, an upper limit of285°K. In general, the ability of the present inventive adhesive to bondto low surface energy surfaces increases as the T_(g) of the rubberphase increases. The T_(g) of the rubber phase is dependent on theweight fraction (i.e., concentration) and the T_(g) of each of thevarious components of the adhesive, as well as the weight fraction andT_(g) of the rubber portion of the copolymer.

The present inventive adhesive can exhibit a 180° peel strength on a lowsurface energy substrate (e.g., HDPE) of at least about 20 N/dm,preferably, at least about 60 N/dm, more preferably at least about 80N/dm, and most preferably at least about 100 N/dm, for example, when theadhesive has a thickness of about 5 mil (125 μm) and is, for example, inthe form of a film (e.g., a transfer tape).

The present adhesive can be used in combination with a backing (e.g., afoam core, a vinyl strip or sheet, etc.) having first and second majorsurfaces, with the adhesive coated on at least a portion of one or bothof the major surfaces. The backing can include a release surface (e.g.,for a tape roll). The backing can also be a foam tape core made of thesame or a different polymodal asymmetric elastomeric block copolymer,and the adhesive can be in the form of at least one co-extruded layer onthe foam tape core. The backing can also be an acrylic foam tape coreand the adhesive in the form of at least one co-extruded layer on thefoam tape core. The backing can be in the form of a foam, with one orboth of its major surfaces being substantially smooth, having an Ravalue less than about 75 micrometers, as measured by laser triangulationprofilometry, and comprising a plurality of microspheres, at least oneand preferably a plurality of which are expandable polymericmicrospheres. Typically, this foam is substantially free of brokenpolymeric microspheres. The present adhesive can also be used incombination with at least one other polymer composition in the form of aplurality of discrete structures bonded to or embedded in the foam.

In another aspect of the invention, an adhesive tape is provided whereinthe backing is a foam formed from a composition comprising a polymodalasymmetric elastomeric block copolymer and the adhesive comprises ablend of two or more polymers, which may be pressure-sensitive,non-pressure-sensitive, or blends thereof. Examples of suitable blendsinclude a block copolymer and an acrylic pressure-sensitive adhesive, ablock copolymer pressure-sensitive adhesive and an acrylic polymer, athermoplastic polymer and a block copolymer pressure-sensitive adhesive,or a thermoplastic polymer and a block copolymer. Preferably, the blockcopolymer is a polymodal asymmetric elastomeric block copolymer. Theadhesive on the tape may be pressure-sensitive.

For an adhesive tape having any foam backing, it can be desirable forthe pressure sensitive adhesive, disposed on one or more surfaces of thefoam backing, to comprise a blend of a polymodal asymmetric elastomericblock copolymer pressure-sensitive adhesive and an acrylicpressure-sensitive adhesive.

Thus, the present invention can include a pressure sensitive adhesivetape that comprises a foam backing having major surfaces and a pressuresensitive adhesive coated on at least a portion of one or more of themajor surfaces, where one or the other or both of the foam backing andthe adhesive comprise a blend of two or more polymers. At least one ofthe polymers comprises:

(a) 100 parts by weight of a polymodal asymmetric elastomeric blockcopolymer;

(b) at least one tackifier;

(c) 0 to about 50 parts by weight of a crosslinking agent; and

(d) 0 to about 300 parts by weight of a plasticizer;

wherein said polymodal asymmetric elastomeric block copolymer has theformula Q_(n) Y and comprises from about 4 to about 40 percent by weightof a polymerized monovinyl aromatic compound and from about 96 to about60 percent by weight of polymerized conjugated diene, wherein:

Q represents an individual arm of said block copolymer and has theformula S-B;

n represents the number of arms Q in said block copolymer and is a wholenumber of at least 3; and

Y is the residue of a multifunctional coupling agent; and furtherwherein:

(a) S is a nonelastomeric polymer segment endblock of a polymerizedmonovinyl aromatic homopolymer, there being at least two differentmolecular weight endblocks in said copolymer, a higher molecular weightendblock and a lower molecular weight endblock, wherein:

(i) the number average molecular weight of said higher molecular weightendblock (Mn)_(H) is in the range of from about 5,000 to about 50,000;

(ii) the number average molecular weight of said lower molecular weightendblock (Mn)_(L) is in the range of from about 1,000 to about 10,000;and

(iii) the ratio (Mn)_(H)/(Mn)_(L) is at least 1.25; and

(b) B is an elastomeric polymer segment midblock which connects each armto the residue of a multifunctional coupling agent (Y) and comprises apolymerized conjugated diene or combination of conjugated dienes.

The present adhesive can exhibit a 90° peel strength on a low surfaceenergy substrate (e.g., HDPE) of at least about 50 N/dm, preferably, atleast about 75 N/dm, more preferably at least about 100 N/dm and mostpreferably at least about 150 N/dm, for example, when the adhesive has athickness of about 3 mil (75μm) to about 5 mil (125 μm) and is, forexample, in the form of an adhesive skin laminated onto, or co-extrudedwith, an adhesive or non-adhesive foam tape core having a thickness ofabout 1 mm. In general, the thicker the adhesive, with or without a foamcore, the higher the bond strength exhibited by the adhesive, up to alimit, such as the cohesive strength of the foam.

Preferably, the tackifier used in the present adhesive is a low acidicor neutral tackifier. As used herein, a low acidic or neutral tackifieris one with an acid number of about 1 mg KOH/g or less, as testedaccording to AMS 360.25 test method. In addition, the tackifierpreferably has a T_(g), as measured by differential scanning calorimeter(DSC), in the range of from about −50° C. to about 200° C. and, morepreferably, from about −30° C. to about 150° C. The T_(g) of theadhesive's rubber phase is dependent, in significant part, on the T_(g)of the tackifier. In general, for a given weight of tackifier, as theT_(g) of the tackifier increases, the T_(g) of the adhesive increases.It is also preferable for the tackifier to have a softening point ofabove 80° C., and more preferably of 90° C. or higher. Preferably, thepresent adhesive comprises at least one tackifier selected from thegroup consisting of hydrogenated mixed aromatic tackifiers,aliphatic/aromatic hydrocarbon liquid tackifiers; napthenic oils,mineral oils, and a mixture of one or more thereof. It can be desirablefor the adhesive to comprise in the range of from about 50 parts toabout 350 parts, preferably, from about 70 parts to about 300 parts and,more preferably, from about 90 parts to about 265 parts by weight of oneor more tackifiers.

The present adhesive can be a radiation crosslinkable composition suchas, for example, by electron beam radiation, ultraviolet radiation,etc., so as to produce a crosslinked polymodal asymmetric elastomericblock copolymer.

In an additional aspect of the invention, an article is provided thatincludes a polymer foam having a substantially smooth surface. The foammay be provided in a variety of shapes, including a rod, a cylinder, asheet, etc. In some embodiments, e.g., where the foam is provided in theform of a sheet, the foam has a pair of major surfaces, one or both ofwhich are substantially smooth. The foam includes a plurality ofmicrospheres, at least one of which is an expandable polymericmicrosphere.

As used herein, a “polymer foam” refers to an article that includes apolymer matrix in which the density of the article is less than thedensity of the polymer matrix alone.

A “substantially smooth” surface refers to a surface having an Ra valueless than about 75 micrometers, as measured by laser triangulationprofilometry according to the procedure described in the Examples,infra. Preferably, the surface has an Ra value less than about 50micrometers, more preferably less than about 25 micrometers. The surfaceis also characterized by the substantial absence of visually observablemacroscopic defects such as wrinkles, corrugations and creases. Inaddition, in the case of an adhesive surface, the surface issufficiently smooth such that it exhibits adequate contact and, thereby,adhesion to a substrate of interest. The desired threshold level ofadhesion will depend on the particular application for which the articleis being used.

An “expandable polymeric microsphere” is a microsphere that includes apolymer shell and a core material in the form of a gas, liquid, orcombination thereof, that expands upon heating. Expansion of the corematerial, in turn, causes the shell to expand, at least at the heatingtemperature. An expandable microsphere is one where the shell can beinitially expanded or further expanded without breaking. Somemicrospheres may have polymer shells that only allow the core materialto expand at or near the heating temperature.

The article is a pressure sensitive adhesive article when the articlehas a surface available for bonding that is either tacky at roomtemperature (i.e., pressure sensitive adhesive articles) or becomestacky after being heated (i.e., heat-activated adhesive articles). Anexample of an adhesive article is a foam that itself is an adhesive, oran article that includes one or more separate adhesive compositionsbonded to the foam, e.g., in the form of a continuous layer or discretestructures (e.g., stripes, rods, filament, etc.), in which case the foamitself need not be an adhesive. Examples of non-adhesive articlesinclude non-adhesive foams and adhesive foams provided with anon-adhesive composition, e.g., in the form of a layer, substrate, etc.,on all surfaces available for bonding.

The foam can be substantially free of urethane crosslinks and ureacrosslinks, thus eliminating the need for isocyanates in thecomposition. An example of such a material for the polymer foam is anacrylic polymer or copolymer. In some cases, e.g., where high cohesivestrength and/or high modulus is needed, the foam may be crosslinked.

The polymer foam preferably includes a plurality of expandable polymericmicrospheres. The foam may also include one or more non-expandablemicrospheres, which may be polymeric or non-polymeric microspheres(e.g., glass microspheres).

Examples of preferred expandable polymeric microspheres include those inwhich the shell is essentially free of vinylidene chloride units.Preferred core materials are materials other than air that expand uponheating.

The foam may contain agents in addition to microspheres, the choice ofwhich is dictated by the properties needed for the intended applicationof the article. Examples of suitable agents include those selected fromthe group consisting of tackifiers, plasticizers, pigments, dyes, solidfillers, and combinations thereof. The foam may also include gas-filledvoids in the polymer matrix. Such voids typically are formed byincluding a blowing agent in the polymer matrix material and thenactivating the blowing agent, e.g., by exposing the polymer matrixmaterial to heat or radiation.

The properties of the article may be adjusted by bonding and/orco-extruding one or more polymer compositions (e.g., in the form ofcontinuous layers or discrete structures such as stripes, rods,filament, etc.) to or into the foam. Both foamed and non-foamedcompositions may be used. A composition may be bonded directly to thefoam or indirectly, e.g., through a separate adhesive.

The article may be used as a “foam-in-place” article. The termfoam-in-place refers to the ability of the article to be expanded orfurther expanded after the article has been placed at a desiredlocation. Such articles are sized and placed in a recessed area or on anopen surface, and then exposed to heat energy (e.g., infrared,ultrasound, microwave, resistive, induction, convection, etc.) toactivate, or further activate, the expandable microspheres or blowingagent. Such recessed areas can include a space between two or moresurfaces (e.g., parallel or non-parallel surfaces) such as found, forexample, between two or more opposing and spaced apart substrates, athrough hole or a cavity. Such open surfaces can include a flat oruneven surface on which it is desirable for the article to expand afterbeing applied to the surface. Upon activation, the foam expands due tothe expansion of the microspheres and/or blowing agent, therebypartially or completely filling the recess or space, or therebyincreasing the volume (e.g. height) of the article above the opensurface.

It can be desirable for the foam to comprise a substantiallyuncrosslinked or thermoplastic polymeric matrix material. It can also bedesirable for the matrix polymer of the foam to exhibit some degree ofcrosslinking. Any crosslinking should not significantly inhibit orprevent the foam from expanding to the degree desired. One potentialadvantage to such crosslinking is that the foam will likely exhibitimproved mechanical properties (e.g., increase cohesive strength)compared to the same foam with less or no crosslinking. In the case offoams having a curable polymer matrix, exposure to heat can alsoinitiate cure of the matrix.

It can further be desirable for the foam-in-place article to comprisemultiple layers, discrete structures or a combination thereof (See, forexample, FIGS. 4-6 and the below discussion thereof), with each layerand discrete structure having a difference in the way it foams-in-place(e.g., using expandable microspheres, blowing agents or a combinationthereof), a difference in the degree to which it can be expanded inplace, or a combination thereof. For example, the concentration ofexpandable microspheres and/or blowing agents can be different, the typeof expandable microspheres and/or blowing agents can be different, or acombination thereof can be used. In addition, for example, one or moreof the layers and discrete structures can be expandable in place whileone or more other layers and discrete structures can be unexpandable inplace.

In yet another aspect of the invention, an article (e.g., an adhesivearticle, as defined above) is provided that comprises a polymer foam (asdefined above) that includes: (a) a plurality of microspheres, at leastone of which is an expandable polymeric microsphere (as defined above),and (b) a polymer matrix that is substantially free of urethanecrosslinks and urea crosslinks. The matrix can include a blend of two ormore polymers in which at least one of the polymers in the blend is apressure sensitive adhesive polymer (i.e., a polymer that is inherentlypressure sensitive, as opposed to a polymer which must be combined witha tackifier in order to form a pressure sensitive composition) and atleast one of the polymers is selected from the group consisting ofsaturated thermoplastic elastomers, unsaturated thermoplasticelastomers, and non-pressure-sensitive-adhesive thermoplastic polymers.It can be desirable for the saturated thermoplastic elastomers used tobe acrylate-insoluble saturated thermoplastic elastomers.

The foam preferably has a substantially smooth surface (as definedabove). In some embodiments, the foam has a pair of major surfaces, oneor both of which may be substantially smooth. The foam itself may be anadhesive. The article may also include one or more separate adhesivecompositions bonded to the foam, e.g., in the form of a layer. Ifdesired, the foam may be crosslinked.

The polymer foam preferably includes a plurality of expandable polymericmicrospheres. It may also include non-expandable microspheres, which maybe polymeric or non-polymeric microspheres (e.g., glass microspheres).The properties of the article may be adjusted by directly or indirectlybonding one or more foamed or non-foamed polymer compositions to thefoam.

The invention also features multi-layer articles that include theabove-described foam articles provided on a major surface of a firstsubstrate, or sandwiched between a pair of substrates. Examples ofsuitable substrates include wood substrates, synthetic polymersubstrates, and metal substrates (e.g., metal foils).

In yet a further aspect of the invention, a method is provided forpreparing an article, where the method includes: (a) melt mixing apolymer composition and a plurality of microspheres, one or more ofwhich is an expandable polymeric microsphere (as defined above), underprocess conditions, including temperature, pressure and shear rate,selected to form an expandable extrudable composition; (b) extruding thecomposition through a die to form a polymer foam (as defined above); and(c) at least partially expanding one or more expandable polymericmicrospheres before the polymer composition exits the die. It can bepreferable for most, if not all, of the expandable microspheres to be atleast partially expanded before the polymer composition exits the die.By causing expansion of the expandable polymeric microspheres before thecomposition exits the die, the resulting extruded foam can be producedto within tighter tolerances, as described below in the DetailedDescription.

It is desirable for the polymer composition to be substantiallysolvent-free. That is, it is preferred that the polymer compositioncontain less than 20 wt. % solvent, more preferably, containsubstantially none to no greater than about 10 wt. % solvent and, evenmore preferably, contain no greater than about 5 wt. % solvent.

In an additional aspect of the invention, another method is provided forpreparing an article that includes: (a) melt mixing a polymercomposition and a plurality of microspheres, one or more of which is anexpandable polymeric microsphere (as defined above), under processconditions, including temperature, pressure and shear rate, selected toform an expandable extrudable composition; and (b) extruding thecomposition through a die to form a polymer foam (as defined above).After the polymer foam exits the die, enough of the expandable polymericmicrospheres in the foam remain unexpanded or, at most, partiallyexpanded to enable the polymer foam to be used in a foam-in-placeapplication. That is, the extruded foam can still be further expanded toa substantial degree at some later time in the application. Preferably,the expandable microspheres in the extruded foam retain most, if notall, of their expandability.

In another aspect of the invention, another method is provided forpreparing an article that includes: (a) melt mixing a polymercomposition and a plurality of microspheres, one or more of which is anexpandable polymeric microsphere (as defined above), under processconditions, including temperature, pressure and shear rate, selected toform an expandable extrudable composition; and (b) extruding thecomposition through a die to form a polymer foam (as defined above)having a substantially smooth surface (as defined above). It is alsopossible to prepare foams having a pair of major surfaces in which oneor both major surfaces are substantially smooth.

Polymers used according to the present invention can preferably possessa weight average molecular weight of at least about 10,000 g/mol, andmore preferably at least about 50,000 g/mol. It can also be preferablefor the polymers used according to the present invention to exhibitshear viscosities measured at a temperature of 175° C. and a shear rateof 100 sec⁻¹, of at least about 30 Pascal-seconds (Pa-s), morepreferably at least about 100 Pa-s and even more preferably at leastabout 200 Pa-s.

The article may be an adhesive article (as defined above), e.g., apressure sensitive adhesive article or a heat-activated adhesivearticle. In some embodiments, the foam itself is an adhesive.

Both the expandable extrudable composition and the extruded foampreferably include a plurality of expandable polymeric microspheres (asdefined above). The extruded foam and the expandable extrudablecomposition may also include one or more non-expandable microspheres,which may be polymeric or non-polymeric microspheres (e.g., glassmicrospheres).

The expandable extrudable composition may be co-extruded with one ormore additional extrudable polymer compositions, e.g., to form a polymerlayer on a surface of the resulting foam. For example, the additionalextrudable polymer composition may be an adhesive composition. Othersuitable additional extrudable polymer compositions include additionalmicrosphere-containing compositions.

The method may also include crosslinking the foam. For example, the foammay be exposed to thermal, actinic, or ionizing radiation orcombinations thereof subsequent to extrusion to crosslink the foam.Crosslinking may also be accomplished by using chemical crosslinkingmethods based on ionic interactions.

The invention provides foam-containing articles, and a process forpreparing such articles, in which the articles can be designed toexhibit a wide range of properties depending upon the ultimateapplication for which the article is intended. For example, the foamcore may be produced alone or in combination with one or more polymercompositions, e.g., in the form of layers to form multi-layer articles.The ability to combine the foam with additional polymer compositionsoffers significant design flexibility, as a variety of different polymercompositions may be used, including adhesive compositions, additionalfoam compositions, removable compositions, layers having differentmechanical properties, etc. In addition, through careful control of thefoaming operation it is possible to produce a foam having a pattern ofregions having different densities.

Both thin and thick foams can be produced. In addition, both adhesiveand non-adhesive foams can be produced. In the latter case, the foam maybe combined with one or more separate adhesive compositions to form anadhesive article. In addition, it is possible to prepare foams from anumber of different polymer matrices, including polymer matrices thatare incompatible with foam preparation processes that rely on actinicradiation-induced polymerization of microsphere-containingphotopolymerizable compositions. Examples of such polymer matrixcompositions include unsaturated thermoplastic elastomers andacrylate-insoluble saturated thermoplastic elastomers. Similarly, it ispossible to include additives such as ultraviolet-absorbing pigments(e.g., black pigments), dyes, and tackifiers that could not be usedeffectively in actinic radiation-based foam processes. It is furtherpossible, in contrast to solvent-based and actinic radiation-based foamprocesses, to prepare foams having a substantially homogeneousdistribution of microspheres. In addition, the present expanded foam(i.e., a foam containing microspheres that have been at least partiallyexpanded) can have a uniform size distribution of the expandedmicrospheres from the surface to the center of the foam. That is, thereis no gradient of expanded microsphere sizes from the surface to thecenter of the foam, e.g., like that found in expanded foams which aremade in a press or a mold. Expanded foams that exhibit such a sizedistribution gradient of their expanded microspheres can exhibit weakermechanical properties than such foams that have a uniform sizedistribution of the expanded microspheres. Oven foaming of these foamcompositions require long residence times in the high temperature ovendue to the poor thermal conductivity of the foams. Long residence timesat high temperatures can lead to polymer and carrier (e.g., releaseliner) degradation. In addition, poor heat transfer can also lead tofoams containing non-uniform expansion, causing a density gradient. Sucha density gradient can significantly decrease the strength and otherwisedetrimentally impact the properties of the foam. The process associatedwith oven foaming is also complicated and usually requires uniqueprocess equipment to eliminate large scale corrugation and buckling ofthe planar sheet. For a reference on oven foaming see, for example,Handbook of Polymeric Foams & Foam Technology, eds: D. Klempner & K. C.Frisch, Hanser Publishers, New York, N.Y., 1991.

Foams with a substantially smooth surface can be produced in a singlestep. Accordingly, it is not necessary to bond additional layers to thefoam in order to achieve a smooth-surfaced article. Substantiallysmooth-surfaced foams are desirable for a number of reasons. Forexample, when the foam is laminated to another substrate, thesubstantially smooth surface minimizes air entrapment between the foamand the substrate. Moreover, in the case of adhesive foams thesubstantially smooth surface maximizes contact with a substrate to whichthe foam is applied, leading to good adhesion.

The extrusion process enables the preparation of multi-layer articles,or articles with discrete structures, in a single step. In addition,when foaming occurs during the extrusion, it is possible, if desired, toeliminate separate post-production foaming processes. Moreover, bymanipulating the design of the extrusion die (i.e., the shape of the dieopening), it is possible to produce foams having a variety of shapes.

In addition, the present method may include heating the article afterextrusion to cause further expansion. The additional expansion may bedue to microsphere expansion, activation of a blowing agent, or acombination thereof.

It is also possible to prepare “foam-in-place” articles by controllingthe process temperature during the initial foam preparation such thatexpansion of the microspheres is minimized or suppressed. The articlecan then be placed at a location of use or application, (e.g., in arecessed area or on an open surface) and heated, or exposed to anelevated temperature to cause microsphere expansion. “Foam-in-place”articles can also be prepared by including a blowing agent in theexpandable extrudable composition and conducting the extrusion processunder conditions insufficient to activate the blowing agent. Subsequentto foam preparation, the blowing agent can be activated to causeadditional foaming.

Other features and advantages of the invention will be apparent from thefollowing description of the preferred embodiments thereof, and from theclaims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1( a) is a plot showing the Ra value obtained by lasertriangulation profilometry for the sample described in Example 12.

FIG. 1( b) is a photomicrograph obtained by scanning electron microscopy(SEM) of the surface of the sample described in Example 12.

FIG. 2( a) is a plot showing the Ra value obtained by lasertriangulation profilometry for the sample described in Example 58.

FIG. 2( b) is a SEM photomicrograph of the surface of the sampledescribed in Example 58.

FIG. 3 is a perspective drawing showing a foam having a patternedsurface.

FIG. 4 is a perspective drawing of an article featuring a foam combinedwith an additional polymer composition.

FIG. 5 is a perspective drawing of an article featuring a foam combinedwith two additional polymer compositions.

FIG. 6 is a perspective drawing of an article featuring a foam combinedwith multiple additional polymer compositions.

FIG. 7 is a schematic drawing of an extrusion process for preparingarticles according to the invention.

FIG. 8 is a plot showing the peel force applied in a direction (MD)parallel to the filament direction as a function of displacement forExamples 73, 77 and 78.

FIG. 9 is a plot showing the peel force applied in a direction (CD)perpendicular to the filament direction as a function of displacementfor Examples 73, 77 and 78.

FIG. 10 is a plot showing the peel force applied in a direction (MD)parallel to the filament direction as a function of displacement forExamples 72, 79, 80 and 81.

FIG. 11 is a plot showing the peel force applied in a direction (CD)perpendicular to the filament direction as a function of displacementfor Examples 72, 79, 80 and 81.

FIGS. 12 a-12 b are SEM photomicrographs of cross-sections, as viewed inthe machine direction (MD) and crossweb direction (CD), respectively, ofthe unoriented foam described in Example 86.

FIGS. 12 c-12 d are SEM photomicrographs of cross-sections, as viewed inthe machine direction (MD) and crossweb direction (CD), respectively, ofthe axially oriented foam described in Example 86.

FIGS. 13 a and 13 b are SEM photomicrographs of cross-sections, asviewed in the machine direction (MD) and crossweb direction (CD),respectively, of the polymer blend foam described in Example 23.

DETAILED DESCRIPTION

The adhesives of the invention are particularly useful for adhering tolow surface energy substrates. As used herein, low surface energysubstrates are those having a surface energy of less than about 45 dynesper centimeter, more typically less than about 40 dynes per centimeter,and most typically less than about 35 dynes per centimeter. Includedamong such materials are polypropylene, polyethylene (e.g., high densitypolyethylene or HDPE), polystyrene and polymethylmethacrylate. Othersubstrates may also have properties of low surface energy due to aresidue, such as an oil residue or a film such as a paint, being on thesurface of the substrate. However, even though the present adhesivebonds well to low surface energy surfaces, the invention is not limitedto being bonded to low surface energy substrates, as it has been foundthat the inventive adhesive can also bond well to higher surface energysubstrates such as, for example, other plastics, ceramics (e.g., glass),metals.

The substrate is selected depending on the particular application inwhich it is to be used. For example, the adhesive can be applied tosheeting products, (e.g., decorative graphics and reflective products),label stock, and tape backings. Additionally, the adhesive may beapplied directly onto a substrate such as an automotive panel, or aglass window so that another substrate or object can be attached to thepanel or window.

The adhesive can also be provided in the form of a pressure-sensitiveadhesive transfer tape in which at least one layer of the adhesive isdisposed on a release liner for application to a permanent substrate ata later time. The adhesive can also be provided as a single coated ordouble coated tape in which the adhesive is disposed on a permanentbacking. Backings can be made from plastics (e.g., polypropylene,including biaxially oriented polypropylene, vinyl, polyethylene,polyester such as polyethylene terephthalate), nonwovens (e.g., papers,cloths, nonwoven scrims), metal foils, foams (e.g., polyacrylic,polyethylene, polyurethane, neoprene), and the like. Foams arecommercially available from various suppliers such as 3M Co., Voltek,Sekisui, and others. The foam may be formed as a coextruded sheet withthe adhesive on one or both sides of the foam, or the adhesive may belaminated to it. When the adhesive is laminated to a foam, it may bedesirable to treat the surface to improve the adhesion of the adhesiveto the foam or to any of the other types of backings. Such treatmentsare typically selected based on the nature of the materials of theadhesive and of the foam or backing and include primers and surfacemodifications (e.g., corona treatment, surface abrasion).

For a single-sided tape, the side of the backing surface opposite thatwhere the adhesive is disposed is typically coated with a suitablerelease material. Release materials are known and include materials suchas, for example, silicone, polyethylene, polycarbamate, polyacrylics,and the like. For double coated tapes, another layer of adhesive isdisposed on the backing surface opposite that where the adhesive of theinvention is disposed. The other layer of adhesive can be different fromthe adhesive of the invention, e.g., a polyacrylic adhesive, or it canbe the same adhesive as the invention, with the same or a differentformulation. Double coated tapes are typically carried on a releaseliner.

Additionally, the present adhesive compositions can be formed into foamsby conventional techniques or, preferably, in accordance with themethods disclosed in PCT Patent Application No. PCT/US99/17344, havingan international filing date of Jul. 30, 1999 and a priority date ofJul. 31, 1998, entitled ARTICLES THAT INCLUDE A POLYMER FOAM AND METHODFOR PREPARING SAME, and which is incorporated herein by reference in itsentirety. Preferred embodiments of such foams and the method of makingthem are described below and illustrated in the drawings. In onepreferred embodiment, the adhesive of the present invention is adheredto one or both surfaces of a polymer foam made in accordance with themethods disclosed in PCT Patent Application No. PCT/US99/17344.

The pressure-sensitive adhesive compositions of the present inventioncan be made from using methods known in the art. They can be made bydissolving the block copolymer, suitable tackifier(s), anyplasticizer(s), and any other additives in a suitable solvent, andcoating onto a substrate (e.g., release liner, tape backing, panel)using conventional means (e.g., knife coating, roll coating, gravurecoating, rod coating, curtain coating, spray coating, air knifecoating). In a preferred embodiment, the pressure-sensitive adhesive isprepared in a solvent free process (i.e., is substantiallysolvent-free). That is, it is preferred that the adhesive contain lessthan 20 wt. % solvent, more preferably, contain substantially none to nogreater than about 10 wt. % solvent and, even more preferably, containno greater than about 5 wt. % solvent. These processes are known andinclude compounding by calendering or roll milling, and extruding (e.g.,single screw, twin screw, disk screw, reciprocating single screw, pinbarrel single screw, etc.). Commercially available equipment such asBRABENDER™ or BANBURY™ internal mixers are also available to batch mixthe adhesive compositions. After compounding, the adhesive may be coatedthrough a die into a desired form, such as a layer of adhesive, or itmay be collected for forming at a later time.

The copolymers useful in making the pressure-sensitive adhesives of theinvention are disclosed in U.S. Pat. No. 5,296,547, incorporated byreference in its entirety herein. The copolymers are polymodalasymmetric elastomeric block copolymers formed by anionicpolymerization. After a copolymer is formed, it may be formed into smallpellets with conventional equipment to facilitate handling of thecopolymer.

As used herein, a tackifier is one that typically has a higher T_(g)than the rubber phase T_(g) of the particular polymodal asymmetricelastomeric block copolymer being used and the addition of the tackifierincreases the T_(g) of the rubber phase of the adhesive composition. Inaddition, as used herein, a plasticizer is one that typically has alower T_(g) than the rubber phase T_(g) of the particular polymodalasymmetric elastomeric block copolymer being used and the addition ofthe plasticizer decreases the T_(g) of the rubber phase of the adhesivecomposition.

In one embodiment of the invention, the copolymer is compounded withconventional tackifying resins and/or plasticizers in amounts sufficientto produce a pressure-sensitive adhesive so that the rubber phase of theresulting pressure-sensitive adhesive has a calculated Fox equationglass transition temperature (T_(g)) of greater than 245°K (Kelvin),preferably greater than about 250°K, and more preferably greater thanabout 255°K, and less than about 300°K, and preferably less than about285°K. Pressure-sensitive adhesives meeting these requirements are foundto have the high adhesion to low energy surfaces such as polyethylenesand polypropylene. In calculating the glass transition temperature, itis assumed that all of the added tackifier(s) goes into the rubberyphase and are miscible within it. The glass transition temperature,T_(g) in degrees Kelvin (°K), of the resulting pressure-sensitiveadhesive is calculated according to the Fox equation shown below:1/T _(g) =w _(c) /T _(g,c) +w _(s) /T _(g,s) +w _(l) /T _(g,l)wherein T_(g,c), T_(g,s), and T_(g,l) represent the glass transitiontemperature of the rubbery phase in the copolymer, the solid tackifier,and the liquid tackifier, respectively, and w_(c), w_(s), and w_(l)represent the weight fractions of the rubbery phase of the copolymer,solid tackifier, and liquid tackifier, respectively, in the adhesive. Asused herein, the term liquid tackifier is meant to include plasticizerssuch as oils that meet the above tackifier definition. The weight of therubbery phase in the copolymer is determined by the amount ofelastomeric component that is added.

The amount of tackifier that is added can also be modified to change themodulus of the adhesive for applications where high shear strength isnot needed and/or desired. The amounts of tackifier may be added tomodify the plateau modulus, G_(0,PSA) of the resultingpressure-sensitive adhesive according to the following equation:G_(0,PSA)=v_(c) ² G_(0,c)wherein v_(c) represents the volume fraction of the rubbery component inthe soft matrix phase comprising the rubbery component and thetackifiers, and G_(0,c) is the modulus of the neat copolymer(elastomer). The modulus of the copolymer can be determined from dynamicmechanical measurements. The present adhesive compositions typicallyhave a calculated plateau modulus of less than 3×10⁶ dyne/cm² (0.3 MPa)and, preferably, less than 10⁶ dyne/cm² (0.1 MPa).

In another embodiment of the invention, a pressure-sensitive adhesivecomprising a blend of a polymodal asymmetric elastomeric block copolymerpressure-sensitive adhesive and an acrylic pressure-sensitive adhesiveis disposed on one or both major surfaces of a foam backing to form apressure-sensitive adhesive tape. Suitable foam backings include thoseare described above as well as the novel foam materials disclosed below.

In yet another embodiment of the invention, an adhesive tape is providedin which the backing is a foam formed from a composition comprising apolymodal asymmetric elastomeric block copolymer and the adhesivecomprises a blend of two or more polymers, which may bepressure-sensitive, non-pressure-sensitive, or blends thereof. Examplesof suitable blends include a block copolymer and an acrylicpressure-sensitive adhesive, a block copolymer pressure-sensitiveadhesive and an acrylic polymer, a thermoplastic polymer and a blockcopolymer pressure-sensitive adhesive, or a thermoplastic polymer and ablock copolymer. The block copolymer compositions preferably include atackifier and are pressure-sensitive adhesives. Preferably, the blockcopolymer is a polymodal asymmetric elastomeric block copolymer.Suitable acrylic polymers, acrylic pressure-sensitive adhesives, blockcopolymers, and thermoplastic polymers include, but are not limited to,those listed below.

Foam Articles

The invention can feature articles that include a polymer foam featuringa polymer matrix and one or more expandable polymer microspheres likethat disclosed in PCT Patent Application No. PCT/US99/17344. Examinationof the foam by electron microscopy reveals that the foam microstructureis characterized by a plurality of enlarged polymeric microspheres(relative to their original size) distributed throughout the polymermatrix. At least one of the microspheres (and preferably more) is stillexpandable, i.e., upon application of heat it will expand furtherwithout breaking. This can be demonstrated by exposing the foam to aheat treatment and comparing the size of the microspheres obtain byelectron microscopy to their pre-heat treated size (also obtained byelectron microscopy).

The foam is further characterized by a surface that is substantiallysmooth, as defined in the Summary of the Invention, above. Lasertriangulation profilometry results and scanning electronphotomicrographs are shown in FIGS. 1 and 2 for representative acrylicfoams having substantially smooth surfaces prepared as described inExamples 12 and 58, respectively, described in further detail below.Each of the photomicrographs of FIGS. 1( b) and 2(b) includes a 100micrometer long measurement bar B. Each of the samples in FIGS. 1( b)and 2(b) have been sectioned, with the surface portion being light andthe sectioned portion being dark.

The foam may be provided in a variety of forms, including a sheet, rod,or cylinder. In addition, the surface of the foam may be patterned. Anexample of such a foam is shown in FIG. 3. Foam 100 is in the form of asheet having a uniform pattern of bumps 102 arranged on the surface ofthe foam. Such articles are prepared by differential foaming, asdescribed in more detail, below. The differential foaming processcreates bumps 102 having a density different from the density of thesurrounding areas 104.

A variety of different polymer resins, as well as blends thereof, may beused for the polymer matrix as long as the resins are suitable for meltextrusion processing. For example, it may be desirable to blend two ormore acrylate polymers having different compositions. A wide range offoam physical properties can be obtained by manipulation of the blendcomponent type and concentration. The particular resin is selected basedupon the desired properties of the final foam-containing article. Themorphology of the immiscible polymer blend that comprises the foammatrix can enhance the performance of the resulting foam article. Theblend morphology can be, for example, spherical, ellipsoidal, fibrillar,co-continuous or combinations thereof. These morphologies can lead to aunique set of properties that are not obtainable by a single componentfoam system. Such unique properties may include, for example,anisotropic mechanical properties, enhanced cohesive strength. Themorphology (shape & size) of the immiscible polymer blend can becontrolled by the free energy considerations of the polymer system,relative viscosities of the components, and most notably the processing& coating characteristics. By proper control of these variables, themorphology of the foam can be manipulated to provide superior propertiesfor the intended article.

FIGS. 13 a and 13 b show SEM photomicrographs of the microstructure ofthe immiscible polymer blend of Example 23 (i.e., 80 wt % of the HotMelt Composition 1 and 20 wt % of Kraton™ D1107). The Kraton™ D1107 wasstained with OsO₄ so as to appear white, which enables this phase to beviewed. These Figures demonstrate that the Kraton™ D1107 phase is acomplex morphology consisting of fibrillar and sphericalmicrostructures, with sizes of approximately 1 μm. In FIG. 13 a, theKraton™ D1107 fibrillar phases are shown in cross-section and appearspherical.

One class of useful polymers includes acrylate and methacrylate adhesivepolymers and copolymers. Such polymers can be formed by polymerizing oneor more monomeric acrylic or methacrylic esters of non-tertiary alkylalcohols, with the alkyl groups having form 1 to 20 carbon atoms (e.g.,from 3 to 18 carbon atoms). Suitable acrylate monomers include methylacrylate, ethyl acrylate, n-butyl acrylate, lauryl acrylate,2-ethylhexyl acrylate, cyclohexyl acrylate, iso-octyl acrylate,octadecyl acrylate, nonyl acrylate, decyl acrylate, and dodecylacrylate. The corresponding methacrylates are useful as well. Alsouseful are aromatic acrylates and methacrylates, e.g., benzyl acrylateand cyclobenzyl acrylate.

Optionally, one or more monoethylenically unsaturated co-monomers may bepolymerized with the acrylate or methacrylate monomers; the particularamount of co-monomer is selected based upon the desired properties ofthe polymer. One group of useful co-monomers includes those having ahomopolymer glass transition temperature greater than the glasstransition temperature of the acrylate homopolymer. Examples of suitableco-monomers falling within this group include acrylic acid, acrylamide,methacrylamide, substituted acrylamides such as N,N-dimethyl acrylamide,itaconic acid, methacrylic acid, acrylonitrile, methacrylonitrile, vinylacetate, N-vinyl pyrrolidone, isobornyl acrylate, cyano ethyl acrylate,N-vinylcaprolactam, maleic anhydride, hydroxyalkylacrylates,N,N-dimethyl aminoethyl (meth)acrylate, N,N-diethylacrylamide,beta-carboxyethyl acrylate, vinyl esters of neodecanoic, neononanoic,neopentanoic, 2-ethylhexanoic, or propionic acids (e.g., available fromUnion Carbide Corp. of Danbury, Conn. under the designation “Vynates”,vinylidene chloride, styrene, vinyl toluene, and alkyl vinyl ethers.

A second group of monoethylenically unsaturated co-monomers which may bepolymerized with the acrylate or methacrylate monomers includes thosehaving a homopolymer glass transition temperature less than the glasstransition temperature of the acrylate homopolymer. Examples of suitableco-monomers falling within this class include ethyloxyethoxy ethylacrylate (Tg=−71° C.) and a methoxypolyethylene glycol 400 acrylate(Tg=−65° C.; available from Shin Nakamura Chemical Co., Ltd. under thedesignation “NK Ester AM-90G”).

A second class of polymers useful for the polymer matrix of the foamincludes acrylate-insoluble polymers. Examples include semicrystallinepolymer resins such as polyolefins and polyolefin copolymers (e.g.,based upon monomers having between 2 and 8 carbon atoms such as lowdensity polyethylene, high density polyethylene, polypropylene,ethylene-propylene copolymers, etc.), polyesters and co-polyesters,polyamides and co-polyamides, fluorinated homopolymers and copolymers,polyalkylene oxides (e.g., polyethylene oxide and polypropylene oxide),polyvinyl alcohol, ionomers (e.g., ethylene-methacrylic acid copolymersneutralized with base), and cellulose acetate. Other examples ofacrylate-insoluble polymers include amorphous polymers having asolubility parameter (as measured according to the Fedors' technique)less than 8 or greater than 11 such as polyacrylonitrile, polyvinylchloride, thermoplastic polyurethanes, aromatic epoxies, polycarbonate,amorphous polyesters, amorphous polyamides, ABS copolymers,polyphenylene oxide alloys, ionomers (e.g., ethylene-methacrylic acidcopolymers neutralized with salt), fluorinated elastomers, andpolydimethyl siloxane.

A third class of polymers useful for the polymer matrix of the foamincludes elastomers containing ultraviolet radiation-activatable groups.Examples include polybutadiene, polyisoprene, polychloroprene, randomand block copolymers of styrene and dienes (e.g., SBR), andethylene-propylene-diene monomer rubber. The third class is not the mostefficient way to do this.

A fourth class of polymers useful for the polymer matrix of the foamincludes pressure sensitive and hot melt adhesives prepared fromnon-photopolymerizable monomers. Such polymers can be adhesive polymers(i.e., polymers that are inherently adhesive), or polymers that are notinherently adhesive but are capable of forming adhesive compositionswhen compounded with tackifiers. Specific examples includepoly-alpha-olefins (e.g., polyoctene, polyhexene, and atacticpolypropylene), block copolymer-based adhesives (e.g., di-block,tri-block, star-block and combinations thereof), polymodal asymmetricelastomeric block copolymers, natural and synthetic rubbers, siliconeadhesives, ethylene-vinyl acetate, and epoxy-containing structuraladhesive blends (e.g., epoxy-acrylate and epoxy-polyester blends).

Also suitable for the polymer matrix are blends of the foregoing classesof polymers.

The expandable microspheres feature a flexible, thermoplastic, polymericshell and a core that includes a liquid and/or gas which expands uponheating. Preferably, the core material is an organic substance that hasa lower boiling point than the softening temperature of the polymericshell. Examples of suitable core materials include propane, butane,pentane, isobutane, neopentane, and combinations thereof.

The choice of thermoplastic resin for the polymeric shell influences themechanical properties of the foam. Accordingly, the properties of thefoam may be adjusted through appropriate choice of microsphere, or byusing mixtures of different types of microspheres. For example,acrylonitrile-containing resins are useful where high tensile andcohesive strength are desired, particularly where the acrylonitrilecontent is at least 50% by weight of the resin, more preferably at least60% by weight, and even more preferably at least 70% by weight. Ingeneral, both tensile and cohesive strength increase with increasingacrylonitrile content. In some cases, it is possible to prepare foamshaving higher tensile and cohesive strength than the polymer matrixalone, even though the foam has a lower density than the matrix. Thisprovides the capability of preparing high strength, low densityarticles.

Examples of suitable thermoplastic resins which may be used as the shellinclude acrylic and methacrylic acid esters such as polyacrylate;acrylate-acrylonitrile copolymer; and methacrylate-acrylic acidcopolymer. Vinylidene chloride-containing polymers such as vinylidenechloride-methacrylate copolymer, vinylidene chloride-acrylonitrilecopolymer, acrylonitrile-vinylidene chloride-methacrylonitrile-methylacrylate copolymer, and acrylonitrile-vinylidenechloride-methacrylonitrile-methyl methacrylate copolymer may also beused, but are not preferred where high strength is desired. In general,where high strength is desired, the microsphere shell preferably has nomore than 20% by weight vinylidene chloride, more preferably no morethan 15% by weight vinylidene chloride. Even more preferred for highstrength applications are microspheres having essentially no vinylidenechloride units.

Examples of suitable commercially available expandable polymericmicrospheres include those available from Pierce Stevens (Buffalo, N.Y.)under the designations “F30D,” “F80SD,” and “F100D.” Also suitable areexpandable polymeric microspheres available from Akzo-Nobel under thedesignations “Expancel 551,” “Expancel 461,” and “Expancel 091.” Each ofthese microspheres features an acrylonitrile-containing shell. Inaddition, the F80SD, F100D, and Expancel 091 microspheres haveessentially no vinylidene chloride units in the shell.

The amount of expandable microspheres is selected based upon the desiredproperties of the foam product. In general, the higher the microsphereconcentration, the lower the density of the foam. In general, the amountof microspheres ranges from about 0.1 parts by weight to about 50 partsby weight (based upon 100 parts of polymer resin), more preferably fromabout 0.5 parts by weight to about 20 parts by weight.

The foam may also include a number of other additives. Examples ofsuitable additives include tackifiers (e.g., rosin esters, terpenes,phenols, and aliphatic, aromatic, or mixtures of aliphatic and aromaticsynthetic hydrocarbon resins), plasticizers, pigments, dyes,non-expandable polymeric or glass microspheres, reinforcing agents,hydrophobic or hydrophilic silica, calcium carbonate, toughening agents,fire retardants, antioxidants, finely ground polymeric particles such aspolyester, nylon, or polypropylene, stabilizers, and combinationsthereof. Chemical blowing agents may be added as well. The agents areadded in amounts sufficient to obtain the desired end properties.

The properties of the article may be adjusted by combining one or morepolymer compositions with the foam. These additional compositions maytake several forms, including layers, stripes, etc. Both foamed andnon-foamed compositions may be used. A composition may be bondeddirectly to the foam or indirectly, e.g., through a separate adhesive.In some embodiments, the additional polymer composition is removablybonded to the foam; such compositions can subsequently be stripped fromthe foam.

Examples of articles featuring combinations of a foam and one or moreadditional polymer compositions are shown in FIGS. 4-6. Referring toFIG. 4, there is shown an article 200 featuring a plurality of foamstripes 202 arranged in a patterned and combined within a separatepolymer layer 204. The density of stripes 202 is different from thedensity of polymer layer 204 surrounding the stripes.

FIG. 5 depicts another article 300 in which a plurality of foam stripes302 are arranged in a pattern and combined within a separate polymerlayer 304. Layer 304, in turn, is bonded to yet another polymer layer306 on its opposite face. The density of stripes 302 is different fromthe density of layer 304 surrounding the stripes.

FIG. 6 depicts yet another article 400 in which a plurality of foamstripes 402 are embedded within a multilayer structure featuring polymerlayers 404, 406, and 408. The density of stripes 402 is different fromthe density of layers 404, 406, and 408.

Preferably, additional polymer compositions are bonded to the foam coreby co-extruding the extrudable microsphere-containing composition withone or more extrudable polymer compositions, as described in greaterdetail, below. The number and type of polymer compositions are selectedbased upon the desired properties of the final foam-containing article.For example, in the case of non-adhesive foam cores, it may be desirableto combine the core with one or more adhesive polymer compositions toform an adhesive article. Other examples of polymer compositionsprepared by co-extrusion include relatively high modulus polymercompositions for stiffening the article (semi-crystalline polymers suchas polyamides and polyesters), relatively low modulus polymercompositions for increasing the flexibility of the article (e.g.,plasticized polyvinyl chloride), and additional foam compositions.

Extrusion Process

Referring to FIG. 7, there is shown an extrusion process for preparingan article that includes a polymer foam featuring a polymer matrix andone or more expandable polymer microspheres. According to the process,polymer resin is initially fed into a first extruder 10 (typically asingle screw extruder) which softens and grinds the resin into smallparticles suitable for extrusion. The polymer resin will eventually formthe polymer matrix of the foam. The polymer resin may be added toextruder 10 in any convenient form, including pellets, billets,packages, strands, and ropes.

Next, the resin particles and all additives except the expandablemicrospheres are fed to a second extruder 12 (e.g., a single or twinscrew extruder) at a point immediately prior to the kneading section ofthe extruder. Once combined, the resin particles and additives are fedto the kneading zone of extruder 12 where they are mixed well. Themixing conditions (e.g., screw speed, screw length, and temperature) areselected to achieve optimum mixing. Preferably, mixing is carried out ata temperature insufficient to cause microsphere expansion. It is alsopossible to use temperatures in excess of the microsphere expansiontemperature, in which case the temperature is decreased following mixingand prior to adding the microspheres.

Where no mixing is needed, e.g., where there are no additives, thekneading step may be omitted. In addition, where the polymer resin isalready in a form suitable for extrusion, the first extrusion step maybe omitted and the resin added directly to extruder 12.

Once the resin particles and additives have been adequately mixed,expandable polymeric microspheres are added to the resulting mixture andmelt-mixed to form an expandable extrudable composition. The purpose ofthe melt-mixing step is to prepare an expandable extrudable compositionin which the expandable polymeric microspheres and other additives, tothe extent present, are distributed substantially homogeneouslythroughout the molten polymer resin. Typically, the melt-mixingoperation uses one kneading block to obtain adequate mixing, althoughsimple conveying elements may be used as well. The temperature,pressure, shear rate, and mixing time employed during melt-mixing areselected to prepare this expandable extrudable composition withoutcausing the microspheres to expand or break; once broken, themicrospheres are unable to expand to create a foam. Specifictemperatures, pressures, shear rates, and mixing times are selectedbased upon the particular composition being processed.

Following melt-mixing, the expandable extrudable composition is meteredinto extrusion die 14 (e.g., a contact or drop die) through a length oftransfer tubing 18 using a gear pump 16 that acts as a valve to controldie pressure and thereby prevent premature expansion of themicrospheres. The temperature within die 14 is preferably maintained atsubstantially the same temperature as the temperature within transfertubing 18, and selected such that it is at or above the temperaturerequired to cause expansion of the expandable microspheres. However,even though the temperature within tubing 18 is sufficiently high tocause microsphere expansion, the relatively high pressure within thetransfer tubing prevents them from expanding. Once the compositionenters die 14, however, the pressure drops. The pressure drop, coupledwith heat transfer from the die, causes the microspheres to expand andthe composition to foam within the die. The pressure within the diecontinues to drop further as the composition approaches the exit,further contributing to microsphere expansion within the die. The flowrate of polymer through the extruder and the die exit opening aremaintained such that as the polymer composition is processed through thedie, the pressure in the die cavity remains sufficiently low to allowexpansion of the expandable microspheres before the polymer compositionreaches the exit opening of the die.

The shape of the foam is dictated by the shape of the exit opening ofthe die 14. Although a variety of shapes may be produced, the foam istypically produced in the form of a continuous or discontinuous sheet.The extrusion die may be a drop die, contact die, profile die, annulardie, or a casting die, for example, as described in Extrusion Dies:Design & Engineering Computation, Walter Michaelis, Hanser Publishers,New York, N.Y., 1984.

It can be preferable for most, if not all, of the expandablemicrospheres to be partially or mostly expanded before the polymercomposition exits the die. By causing expansion of the expandablepolymeric microspheres before the composition exits the die, theresulting extruded foam can be produced to within tighter density andthickness (caliper) tolerances. A tighter tolerance is defined as themachine (or longitudinal) direction and crossweb (or transverse)direction standard deviation of density or thickness over the averagedensity or thickness (σ/x), respectively. The σ/x that is obtainableaccording to the present invention can be less than about 0.2, less thanabout 0.1, less than about 0.05, and even less than about 0.025. Withoutany intention to be so limited, the tighter tolerances obtainableaccording to the present invention is evidenced by the followingexamples.

As shown in FIG. 7, the foam may optionally be combined with a liner 20dispensed from a feed roll 22. Suitable materials for liner 20 includesilicone release liners, polyester films (e.g., polyethyleneterephthalate films), and polyolefin films (e.g., polyethylene films).The liner and the foam are then laminated together between a pair of niprollers 24. Following lamination or after being extruded but beforelamination, the foam is optionally exposed to radiation from an electronbeam source 26 to crosslink the foam; other sources of radiation (e.g.,ion beam, thermal and ultraviolet radiation) may be used as well.Crosslinking improves the cohesive strength of the foam. Followingexposure, the laminate is rolled up onto a take-up roll 28.

If desired, the smoothness of one or both of the foam surfaces can beincreased by using a nip roll to press the foam against a chill rollafter the foam exits die 14. It is also possible to emboss a pattern onone or both surfaces of the foam by contacting the foam with a patternedroll after it exits die 14, using conventional microreplicationtechniques, such as, for example, those disclosed in U.S. Pat. No.5,897,930 (Calhoun et al.), U.S. Pat. No. 5,650,215 (Mazurek et al.) andthe PCT Patent Publication No. WO 98/29516A (Calhoun et al.). Thereplication pattern can be chosen from a wide range of geometricalshapes and sizes, depending on the desired use of the foam. Thesubstantially smooth surface of the extruded foam enablesmicroreplication of the foam surface to a higher degree of precision andaccuracy. Such high quality microreplication of the present foam surfaceis also facilitated by the ability of the foam to resist being crushedby the pressure exerted on the foam during the microreplication process.Microreplication techniques can be used without significantly crushingthe foam because the foam includes expandable microspheres that do notcollapse under the pressure of the microreplication roll, compared tofoaming agents like gas.

The extrusion process may be used to prepare “foam-in-place” articles.Such articles find application, for example, as gaskets or othergap-sealing articles, vibration damping articles, tape backings,retroreflective sheet backings, anti-fatigue mats, abrasive articlebackings, raised pavement marker adhesive pads, etc. Foam-in-placearticles may be prepared by carefully controlling the pressure andtemperature within die 14 and transfer tubing 18 such that microsphereexpansion does not occur to any appreciable extent. The resultingarticle is then placed in a desired area, e.g., a recessed area or opensurface and heated at, or exposed to, a temperature sufficiently high tocause microsphere expansion.

Foam-in-place articles can also be prepared by incorporating a chemicalblowing agent such as 4,4′-oxybis(benzenesulfonylhydrazide) in theexpandable extrudable composition. The blowing agent can be activatedsubsequent to extrusion to cause further expansion, thereby allowing thearticle to fill the area in which it is placed.

The extrusion process can also be used to prepare patterned foams havingareas of different densities. For example, downstream of the point atwhich the article exits the die, the article can be selectively heated,e.g., using a patterned roll or infrared mask, to cause microsphereexpansion in designated areas of the article.

The foam may also be combined with one or more additional polymercompositions, e.g., in the form of layers, stripes, rods, etc.,preferably by co-extruding additional extrudable polymer compositionswith the microsphere-containing extrudable compositions. FIG. 7illustrates one preferred co-extrusion process for producing an articlefeaturing a foam sandwiched between a pair of polymer layers. As shownin FIG. 7, polymer resin is optionally added to a first extruder 30(e.g., a single screw extruder) where it is softened and melt mixed. Themelt mixed resin is then fed to a second extruder 32 (e.g., a single ortwin screw extruder) where they are mixed with any desired additives.The resulting extrudable composition is then metered to the appropriatechambers of die 14 through transfer tubing 34 using a gear pump 36. Theresulting article is a three-layer article featuring a foam core havinga polymer layer on each of its major faces.

It is also possible to conduct the co-extrusion process such that atwo-layer article is produced, or such that articles having more thanthree layers (e.g., 10-100 layers or more) are produced, by equippingdie 14 with an appropriate feed block, or by using a multi-vaned ormulti-manifold die. Tie layers, primers layers or barrier layers alsocan be included to enhance the interlayer adhesion or reduce diffusionthrough the construction. In addition, we also can improve theinterlayer adhesion of a construction having multiple layers (e.g., A/B)of different compositions by blending a fraction of the A material intothe B layer (A/AB). Depending on the degree of interlayer adhesion willdictate the concentration of A in the B layer. Multilayer foam articlescan also be prepared by laminating additional polymer layers to the foamcore, or to any of the co-extruded polymer layers after the articleexits die 14. Other techniques which can be used include coating theextruded foam (i.e., extrudate) with stripes or other discretestructures.

Post processing techniques, which may include lamination, embossing,extrusion coating, solvent coating, or orientation, may be performed onthe foam to impart superior properties. The foams may be uni-axially ormulti-axially oriented (i.e., stretched in one or more directions) toproduce foam structures that contain microvoids between or a separationof the foam matrix and the expandable microspheres (See Examples 85-92).FIGS. 12 a-12 d show SEM micrographs of the microstructure of the foamof Example 86, before (FIGS. 12 a and 12 b) and after (FIGS. 12 c and 12d) uniaxial orientation. FIGS. 12 a and 12c are cross-sectional views ofthe foam microstructure as seen in the machine direction (MD). That is,for FIGS. 12 a and 12 c, the foam was sectioned perpendicular to thedirection the foam flows as it exits the die and viewed in the directionof flow. FIGS. 12 b and 12 d are cross-sectional views of the foammicrostructure as seen in the crossweb direction (CD). That is, forFIGS. 12 b and 12 d, the foam was sectioned parallel to the directionthe foam flows as it exits the die and viewed in the directionperpendicular to the direction of flow.

The selection of the foam matrix, expandable microspheretype/concentration and orientation conditions can affect the ability toproduce microvoided foam materials. Orientation conditions include thetemperature, direction(s) of stretch, rate of stretch, and degree ofstretch (i.e., orientation ratio). It is believed that the interfacialadhesion between the foam matrix and the expandable microspheres shouldbe such to allow at least some debonding to occur around themicrospheres upon stretching (i.e., orientation). It is also believedthat poor interfacial adhesion can be preferable. Furthermore, it has befound desirable for the foam matrix to be capable of undergoingrelatively high elongation (e.g., at least 100%). Orientation of thefoam samples can cause a reduction in density of the foam (e.g., up toabout 50%) due to the formation of microvoids between the foam matrixand the microspheres that form during orientation. Microvoids can remainafter the stretching (orientation) process or they can disappear (i.e.,collapse but the interface remains unbonded). In addition, delaminationbetween the foam matrix and the microspheres, with or without anoticeable density reduction, can result in a significant alteration ofthe mechanical properties of the foam (e.g., increase in flexibility,reduction in stiffness, an increase in softness of foam, etc.).Depending on the ultimate foam application, the material selection andthe orientation conditions can be selected to generate desiredproperties.

It can be desirable for the extrudable polymer composition to becrosslinkable. Crosslinking can improve the cohesive strength of theresulting foam. It may be desirable for the crosslinking of theextrudable polymer to at least start between the melt mixing step andexiting of the polymer through the die opening, before, during or afterfoaming, such as by the use of thermal energy (i.e., heat activatedcuring). Alternatively or additionally, the extrudable polymercomposition can be crosslinked upon exiting the die such as, forexample, by exposure to thermal, actinic, or ionizing radiation orcombinations thereof. Crosslinking may also be accomplished by usingchemical crosslinking methods based on ionic interactions. The degree ofcrosslinking can be controlled in order to influence the properties ofthe finished foam article. If the extruded polymer is laminated, asdescribed herein, the polymer extrudate can be crosslinked before orafter lamination. Suitable thermal crosslinking agents for the foam caninclude epoxies and amines. Preferably, the concentrations aresufficiently low to avoid excessive crosslinking or gel formation beforethe composition exits the die.

Use

The foam-containing articles are useful in a variety of applicationsincluding, for example and not by way of limitation, aerospace,automotive, and medical applications. The properties of the articles aretailored to meet the demands of the desired applications. Specificexamples of applications include vibration damping articles, medicaldressings, tape backings, retroreflective sheet backings, anti-fatiguemats, abrasive article backings, raised pavement marker adhesive pads,gaskets, sealants, signs, nameplates, plaques, appliances, etc.

The following non-limiting examples serve to further illustrate specificembodiments of the invention. All of the materials are reported in partsby weight (parts).

Test Methods

Unless otherwise stated, the tapes were conditioned without a protectiveliner in a constant temperature and humidity (CTH) room (22° C.; 50%relative humidity) for about 24 hours before testing. All roomtemperature peel adhesion testing and room temperature static shearmeasurements were also conducted in the CTH room. Elevated temperaturestatic shear (70° C.) static shear testing was conducted in a preheatedconvection oven.

180° C. Peel Adhesion

A pressure-sensitive adhesive transfer tape was adhered to a 35micrometer thick biaxially oriented polyethylene terephthalate filmusing a hand held 2 kg hard rubber roller to form a test tape. The sideof the tape that faced the e-beam radiation was laminated to apolyethylene terephthalate film. The test tape was slit to a width of1.27 cm and adhered to a test panel using two total passes of a 2 kg(4.5 lb) hard rubber roller. The test panels were cleaned by wipingtwice with a tissue soaked with isopropanol and drying. Panels used wereglass (GL), polypropylene (PP), high density polyethylene (PE),stainless steel (SS), and a metal panel painted with RK-7072 automotivepaint obtained from DuPont Co.(Paint). Plastic panels were obtained fromAeromat Plastics, Burnsville, Minn. and stainless steel panels wereobtained from Assurance Mfg., Minneapolis, Minn. After conditioning thebonded assembly for at least 24 hours in the CTH room, and the assemblyis tested for 180° peel adhesion using an IMASS slip/peel tester (Model3M90, commercially available from Instrumentors Inc., Strongsville,Ohio) at a rate of 30.5 cm/min (12 in/min) over a 10 second datacollection time. Test results are reported in Newtons/decimeter (N/dm).

90° Peel Adhesion

A 1.27 cm by 11.4 cm strip of pressure-sensitive adhesive tape on arelease liner was laminated to a 1.6 cm wide strip of 0.127 mm thickaluminum foil. The release liner was then removed and the tape isapplied to a cleaned test panel (types of panels described above) usingfour total passes of a 2 kg (4.5 lb) hard rubber roller to form a testassembly. If the tape was a double coated tape or a foam tape, the sideof the tape having the test adhesive was adhered to the test panel. Eachtest assembly was aged at one of the following conditions beforetesting:

-   -   1 hour at room temperature (22° C.) and 50% relative humidity        (1H-RT)    -   24 hours room temperature (22° C.) and 50% relative humidity        (24H-RT)    -   3 days at room temperature (22° C.) and 50% relative humidity        (3D-RT)    -   3 days at 70° C. (3D-70° C.)    -   5 days at room temperature (22° C.) and 50% relative humidity        (5D-RT)    -   5 days at 70° C. (5D-70° C.).    -   7 days at room temperature (22° C.) and 50% relative humidity        (7D-RT)    -   7 days at 70° C. (7D-70° C.)    -   5 days at 100° C. and 100% humidity—5D-100/100

After aging, the panel was mounted in an Instron™ Tensile Tester suchthat the tape was pulled off at a 90° angle at a speed of 30.5 cm perminute unless otherwise indicated. Results were determined in pounds per0.5 inch, and converted to Newtons per decimeter (N/dm).

Static Shear

A 1.27 cm wide pressure-sensitive adhesive tape on a release liner waslaminated to a 1.6 cm wide strip of 0.127 mm thick aluminum foil. Therelease liner was removed and the tape was adhered to a clean rigidanodized aluminum panel with four passes of a 2 kg (4.5 lb) hard rubberroller such that a 1.27 cm by 2.54 cm portion of the tape was in firmcontact with the panel and one end portion of the tape extending beyondthe panel. The prepared panel was conditioned at room temperature, i.e.,about 22° C. for at least 1 hour. The panel was then either hung in aconstant temperature and humidity environment (22° C.; 50% relativehumidity) for RT shear testing or in an air circulating oven maintainedat 70° C. (70° C.). The sample was positioned 2 degrees from thevertical to prevent a peel mode failure. A 1000 gram weight was hungfrom the free end of the sample for the case of RT static shear testingand a 500 gram weight was hung for the 70° C. static shear testing. For70° C. shear testing the panel was equilibrated in the oven for 10 minbefore the 500 g weight was hung from the free end of the tape. The timerequired for the weight to fall off was recorded in minutes. If nofailure occurred within 10,000 minutes, the test was discontinued andresults were recorded as 10000, indicating the that time is actuallygreater than 10,000 minutes. If the tape had fallen off in fewer than10,000 minutes, the mode of failure was noted as cohesive failure withinthe adhesive, and indicated in the Table with a “C” or noted as adhesivefailure when the adhesive pulled cleanly from the panel, and indicatedin the Table with a “P”.

Glossary of Materials

Regalite™ S101—Hydrogenated mixed aromatic tackifier resin availablefrom Hercules Inc., Wilmington, Del.

Regalite™ R125—Hydrogenated mixed aromatic tackifier resin availablefrom Hercules Inc., Wilmington, Del.

Escorez™ 2520 Aliphatic/Aromatic (mixed) hydrocarbon liquid tackifieravailable from Exxon Chemical Company, Houston, Tex.

Escorez™ 1310 Hydrocarbon aliphatic tackifier available from ExxonChemical Company, Houston, Tex.

Shellflex™ 371—Napthenic Oil available from Shell Chemical Company,Houston, Tex.

Wingtack Plus™—aromatically modified petroleum resin available fromGoodyear Tire & Rubber Company, Akron, Ohio

Zonarez™ A-25—A poly alpha-pinene resin available from Arizona ChemicalCompany, Panama City, Fla.

Irganox™ 1010—Antioxidant/Stabilizer available from Ciba SpecialtyChemicals Corporation, Tarrytown, N.Y.

Tinuvin™ 328—Ultra Violet (UV) light Stabilizer available from CibaSpecialty Chemicals Corporation, Tarrytown, N.Y.

Block Copolymer Preparation

A polymodal asymmetric elastomeric block copolymer was preparedaccording to the method for Polymer B described in U.S. Pat. No.5,393,787, which is incorporated herein by reference in its entirety.The polymer had number average molecular weights of 4,000 and 21,500 forthe two endblocks, 135,400 for the arm, and 1,087,000 for the star. Thenumber average molecular weight were measured according using a HewlettPackard Model 1082B size exclusion chromatograph equipped with twobimodal Zorbax PSM kits (two columns at 60-S Angstroms and two columnsat 1000-S Angstroms) using the test method described in U.S. Pat. No.5,296,547. The percent of high molecular weight arms was estimated to beabout 40%, and the weight percent styrene was determined from the chargeratio of styrene and isoprene to be 6%. The copolymer was processed intopellets suitable for extrusion or other processing.

Hot Melt Composition A

A hot melt pressure-sensitive adhesive (PSA) composition was prepared byfeeding a dry mixture of 100 parts of pellets of the above describedcopolymer, 2 parts an antioxidant (Irganox 1010), and 2 parts of a UVstabilizer (Tinuvin 328) to the first zone of a 30 mm Werner &Pfleiderer (ZSK-30) co-rotating twin screw extruder having three feedports. The extruder screw had 12 sections with forward kneading insections 2,4,6, and 8, and conveying in the remainder of the sections.The pellet mixture was fed to the extruder at a rate of about 2.06kg/hr. Molten tackifier (Regalite™S101) at a temperature of 163° C. waspumped into zone 5 at a feed rate of 2.31 kg/hr, and oil (Escorez™ 2520)was pumped into zone 7 at a feed rate of 0.24 kg/hr. Screw speed wasapproximately 275 RPM resulting in operating pressures of about 3.4 MPa(500 psi). The total output of the extruder was about 4.54 kg/hr. Thetemperature was 121° C. in zones 1 and 2, 163° C. in zones 3 and 4, 179°C. in zones 5 and 6, and 188° C. in zones 7-12. The exit hose,maintained at 188° C., conveyed the molten composition to a siliconerelease lined box where it cooled under ambient conditions.

Hot Melt Composition B

A hot melt pressure-sensitive adhesive (PSA) composition was preparedfollowing the procedure for Hot Melt Composition A except the feed ratesof the copolymer, Regalite™S101 tackifier, and Escorez™2520 oil were1.53 kg/hr, 2.35 kg/hr, and 0.66 kg/hr, respectively.

Hot Melt Composition C

A hot melt pressure sensitive adhesive (PSA) composition was preparedfollowing the procedure for Hot Melt Composition A above except the feedrates of the copolymer, Regalite™S101 tackifier, and Escorez™2520 oilwere 1.53 kg/h, 2.71 kg/h, and 0.29 kg/h, respectively.

Hot Melt Composition D

A hot melt pressure-sensitive adhesive composition was prepared bymixing 97 parts isooctylacrylate, 3 parts acrylic acid, 0.15 part 2,2dimethoxy-2-phenylacetophenone (Irgacure™651 available from Ciba Geigy)and 0.03 parts of IOTG (isooctyl thioglycolate). The composition wasplaced into film packages measuring approximately 10 cm by 5 cm by 0.5cm thick packages as disclosed in U.S. Pat. No. 5,804,610 incorporatedherein in its entirety by reference. The packaging film was a 0.0635thick ethylene vinylacetate copolymer (VA-24 Film available from CT Filmof Dallas, Tex.) The packaged composition was immersed in a water bathand at the same time exposed to ultraviolet radiation at an intensity of3.5 milliWatts per square centimeter and a total energy of 1795milliJoules per square centimeter as measured in NIST units to form apackaged pressure-sensitive-adhesive.

Hot Melt Composition E

A hot melt pressure-sensitive adhesive composition was preparedfollowing the procedure for Hot Melt Composition D except that 90 partsof 2-ethylhexylacrylate and 10 parts of acrylic acid were used.

Hot Melt Composition F

A pressure-sensitive adhesive composition was prepared following theprocedure for Hot Melt Composition D except that the composition was 93parts of 2-ethylhexyl acrylate and 7 parts of acrylic acid and the totalenergy was 1627 milliJoules per square centimeter as measured in NISTunits.

Hot Melt Composition G

A pressure-sensitive adhesive composition was prepared following theprocedure for Hot Melt Composition D except that the composition was 90parts of 2-ethylhexyl acrylate and 10 parts of acrylic acid.

Hot Melt Composition H

A pressure-sensitive adhesive composition was prepared following theprocedure for Hot Melt Composition D except that the composition was 95parts of 2-ethylhexyl acrylate and 5 parts of acrylic acid.

Hot Melt Composition I

A pressure-sensitive adhesive composition was prepared following theprocedure for Hot Melt Composition A except the feed rates for thecopolymer, Regalite™ S 101 tackifier, and Escorez™ 2520 oil were 1.52Kg/hr, 2.48 Kg/hr and 0.5 Kg/hr, respectively.

Hot Melt Composition J

A pressure-sensitive adhesive composition was prepared following theprocedure for Hot Melt Composition D except that the composition was 97parts of 2-ethylhexyl acrylate and 3 parts of acrylic acid.

Hot Melt Composition K

A pressure-sensitive adhesive composition was prepared following theprocedure for Hot Melt Composition A with the following exceptions: Hotmelt composition J was fed into an open port at zone #2 with a 51 mmsingle screw extruder at a rate of 3.9 Kg/hr. The block copolymer pelletmixture described in Hot Melt Composition A was fed at 1.2 Kg/hr. A 4 to1 by weight blend of Regalite™ 1125 and Escorez™ 180 (produced by Exxon)was substituted for Regalite™ S101 and was fed at 2 Kg/hr. Also, noEscorez™ 2520 oil was added.

EXAMPLES 1-10

Pressure-sensitive adhesive compositions were prepared by adding theamounts of the block copolymer, tackifier (Regalite™S101), oil(Escorez™2520), and antioxidant (Irganox 1010), all in parts by weight,shown in Table 1 to a glass jar. Sufficient toluene was added to eachglass jar to form a 40% by weight solution. After the dry materials weredissolved in the toluene by sitting overnight on a shaker, the solutionswere each knife coated onto a 50 micrometer (2 mil) silicone coatedpolyethylene terephthalate (PET) release liner to a thickness of about312 micrometers. The coatings were dried in a preheated air circulatingoven set at 70° C. for 15 minutes to remove the solvent, leaving a 127micrometer thick adhesive forming an adhesive transfer tape. Theadhesive tapes were then covered with a protective silicone coated paperrelease liner to await further processing.

The protective paper release liner was then removed and each example wasirradiated with electron beam radiation with a dose of 4 Mrad and 175 kVusing an Electrocurtain CB-300 electron beam system (available fromEnergy Sciences Inc., Wilmington, Mass.) to cross-link the adhesive. Thetapes were tested for 180° Peel Adhesion and Static Shear according tothe above test procedures. Test results, the Fox equation glasstransition temperature (T_(g)), and the plateau modulus are shown inTable 1 for each example.

TABLE 1 Regalite ™ Escorez ™ Irganox ™ 180° Peel Adhesion - N/dm StaticShear Coploymer S101 2520 1010 24H-RT 5D-70° C. Min Ex Fox Tg ° K. G₀dyne/cm² Parts Parts Parts Parts Glass PP PE Glass PP PE RT 70° C. 1 258800000 100 94.5 4.9 2 152 115 68 NT NT NT 10000 NT 2 258 600000 100 97.231.6 2 177 120 79 NT NT NT 10000 NT 3 258 350000 100 103.5 93.3 2 206126 84 NT NT NT 1269 P NT 4 263 600000 100 116.7 12.1 2 184 124 68 150119  67 10000 10000 5 263 350000 100 129.1 67.7 2 254 158 113 NT NT NT5694 P NT 6 263 100000 100 174.6 272.8 2 209 188 133 NT NT NT 1049 C NT7 268 350000 100 153.7 43.0 2 191 180 121 222 152 111 10000 10000 8 268100000 100 220.7 226.6 2 213 203 133 NT NT NT 1055 C NT 9 273 350000 100177.5 19.3 2 224 194 64 254 201 152 10000 10000 10 273 100000 100 265.2182.2 2 286 273 156 NT NT NT 1579 C NT NT—Not tested

The data in Table 1 show that the adhesives of the invention haveexcellent adhesion to low energy surfaces (polyethylene andpolypropylene) as well as high energy surfaces (glass), and can beformulated to have excellent shear strength at elevated temperatures.Additionally, the data in Examples 6,7, and 9 show that elevatedtemperature aging of the samples prior to testing had no deleteriouseffect on the adhesion properties.

EXAMPLES 11-16

Pressure-sensitive adhesive transfer tapes were prepared following theprocedure for Example 1 except that varying amounts of the differenttackifiers and oils shown in Table 2 were used. The adhesive tapes wereirradiated at a dose of 4 Mrad at 225 kV. 180° Peel Adhesion (24H-RT)and Static Shear testing results are shown in Table 2.

TABLE 2 Regalite ™ Shellflex ™ 180° Peel Static Shear Fox G₀ S101 371Adhesion N/dm Min Ex Tg ° K. Dynes/cm² Parts Parts Glass PP PE RT 70° C.11 263 600000 122.8 6.0 141 107 74 10000 10000 12 263 500000 135.2 14.6152 131 79 10000 7466 P 13 265.5 600000 127.5 1.3 168 132 88 10000 9539P 14 265.5 500000 140.4 9.4 172 128 95 10000 8287 P 15 265.5 350000169.2 27.5 178 139 98 10000 2042 P 16 268 500000 145.5 4.3 193 147 10210000 10000The data in Table 2 illustrates the utility of a different oil incompositions of the invention.

EXAMPLES 17-24

Pressure-sensitive adhesive tapes were prepared following the procedurefor Example 1 except that a different tackifying resin was used in theamounts indicated in Table 3 and 2 parts of a UV stabilizer (Tinuvin328) were added in addition to the antioxidant. The tapes wereirradiated with a dose of 8 Mrad at 175 kV and tested for 180° peeladhesion (24H-RT) and static shear. Results are also shown in the Table3.

TABLE 3 Regalite ™ Escorex ™ 180° Peel Static Shear Fox G₀ R125 2520Adhesion N/dm Min Ex Tg ° K. Dynes/cm² Parts Parts Glass PP PE RT 70° C.17 263 800000 90.4 9.0 150 142 67 10000 10000 18 265 800000 95.7 3.6 184142 78 10000 10000 19 265 600000 100.9 27.9 189 147 85 3254 P 10000 20268 600000 110.0 18.8 218 120 101 6124 P 10000 21 268 350000 124.7 72.0205 129 115 1126 P 219 P 22 270 600000 116.0 12.8 224 131 112 6456 P10000 23 271 680000 115.5 0 244 224 112 10000 10000 24 268 760000 104.80 233 191 98 10000 10000

EXAMPLES 25-31

For Examples 25-28, a composition was prepared by mixing 100 parts ofcopolymer pellets, 2 parts of Irganox™1010 antioxidant, and 2 of partsTinuvin™328 UV stabilizer (Feed I). The mixture was fed to zone 1 of a30 mm Werner & Pfleiderer co-rotating twin screw extruder (Model ZSK-30)having 12 section screws with forward kneading in sections 2, 4, 6, and8, and conveying sections in the remaining sections. A molten tackifier(Regalite™S101), heated to about 177° C., was fed into zone 5 using aHelicon pump (Feed II), and an oil (Escorez™2520) was fed into zone 7(Feed III). The feed rates for each example are shown in Table 4. Thescrew speed was approximately 300 RPM resulting in operating pressuresof about 3.4-5.5 MPa (500-800 psi) and a total flow rate in the range ofabout 2.72 to 3.62 kg/h. The temperature was 149° C. in zones 1 and 2,157° C. in zones 3 and 4, 160° C. in zones 5 and 6, and 163° C. in zones7-12. The exit hose, maintained at 165.5° C., conveyed the moltenpressure-sensitive adhesive composition to a 0.5 mm (20 mil) shimmed,15.24 cm wide drop die maintained at 165.5° C. where the extrudate wascollected as a 125 micrometer thick pressure-sensitive adhesive transfertape between two silicone coated paper release liners.

One of the liners was then removed and each example was irradiated withelectron beam radiation using an Electrocurtain CB-300 electron beamsystem (available from Energy Sciences Inc., Wilmington, Mass.).Examples 25-28 were irradiated with 225 kV and a dose of 6 Mrads.

Adhesive tapes for Examples 29-31 were prepared following the procedurefor Example 25 except that the tackifier used was Escorez™1310 LC andthe oil used was Shellflex™371. Feed rates are shown in Table 4. TheExamples were irradiated with a dose of a 4 Mrad at 225 kV to cross linkthe adhesive.

Test results for 180° peel adhesion (24H-RT) and static shear of theadhesives are shown in Table 4.

TABLE 4 180° Peel Static shear - Feed I Feed II Feed III Adhesion - N/dmmin Ex Kg/h Kg/h Kg/h Glass PP PE RT 70° C. 25 1.215 1.365 0.141 168 13881 10000 10000 26 0.943 1.279 0.499 305 193 141 10000 185 P 27 0.9431.393 0.39 295 205 145 10000 107 P 28 1.116 1.601 0.005 213 161 10310000 10000 29 1.606 2.009 0 161 152 88 10000 10000 30 1.238 2.059 0.331149 146 88 10000  38 C 31 0.930 1.606 0.191 180 176 95 10000  46 C

That data in Table 4 illustrate the utility of hot melt coatedcompositions of the invention on low energy surfaces.

COMPARATIVE EXAMPLES C1-C5

A pressure-sensitive adhesive having 100 parts of copolymer, 40 parts ofa tackifier (Wingtack™Plus) and 30 parts of a plasticizer (Zonarex™A-25) was prepared following the procedure for Example 1. The Fox GlassTransition Temperature (Tg) of the adhesive was 240.5°K. Portions of theadhesive were irradiated with electron beam radiation as voltages anddoses shown in Table 5. The adhesives were then tested for 180° peeladhesion and d static shear; results are shown in Table 5.

TABLE 5 E-beam 180° Peel Static Irradiation Adhesion - N/dm Shear-minExample KV Mrad Glass PP PE RT 70° C. C1 None None 78 66 14 10000 1615CC2 150 5 68 57 11 10000 10000 C3 175 4 63 58 14 10000 10000 C4 175 5 5956 17 10000 10000 C5 225 4 59 57 14 10000 10000

The data in Table 5 and from the previous examples illustrate thesuperior adhesion that adhesives of the invention have on low energysurfaces.

EXAMPLES 32-37

The pressure-sensitive adhesive foam tapes were prepared by laminatingthe each of the cross-linked adhesive transfer tapes of Examples 11-16to a one mm thick acrylic foam that is the core of a pressure-sensitiveadhesive tape construction (VHB 4941 available from 3M Company, St.Paul, Minn.) using four passes of a 2 kg (4.5 lb) hard rubber rollersuch that the side which faced the electron beam radiation was againstone of the major surfaces of the foam. The tapes were tested for staticshear and 90° peel adhesion according to the above test procedures onthe substrates indicated. Test results are shown in Table 6.

TABLE 6 90° peel adhesion - N/dm Static shear Transfer 5D-RT 5D-70° C.Min Ex Tape Steel PP PE Steel PP PE 70° C. 32 Ex 11 401 427 168 284 385203 10000 33 Ex 12 364 508 182 291 409 214 10000 34 Ex 13 382 482 196315 412 205 10000 35 Ex 14 485 550 214 356 457 242 10000 36 Ex 15 394511 198 408 489 252 10000 37 Ex 16 541 485 198 389 529 264 10000

The data in Table 6 illustrate acrylic foam tapes of the invention.

The foam tape of Example 35 was also tested on other commerciallyavailable plastic substrates for 90° peel adhesion. The substrates werecleaned as described above and were obtained from Aeromat Plastics,Burnesville, Minn. Test assemblies were conditioned at 3D-RT and 3D-70°C. Test results are shown in Table 7.

TABLE 7 90° peel adhesion Plastic 3D-RT 3D-70° C. ABS 408 595 LDPE 280177 PVC 411 485 Polystyrene 471 490 Polycarbonate* 508 548 PMMA** 501620 Nylon 382 481 *Lexan ™ **Plexiglas ™

The data in Table 7 illustrate the utility of the invention on variousplastic substrates.

EXAMPLES 38-39

An expandable pressure-sensitive adhesive composition was prepared byfeeding a dry blended mixture having 67 parts of copolymer, 33 partsRegalite™S101 tackifier, 1.34 parts Irganox™1010, and 1.34 partsTinuvin™328 into zone 1 of 25 mm Berstorff twin screw extruder (ModelZE-25, L/D=36:1, Florence, Ky.) using a K-tron gravimetric feeder (ModelF-1, S/N:930601, Pitman, N.J.) such that the feed rate was 2.29 kg/h. Agrid melter (ITW Dynatech Model O22S, Burlington, Mass.) was used tofeed 1.57 kg/h of molten Regalite™S101 at a temperature of 182° C. intozone 3. A Zenith gear pump (1.2 cm³/rev. Zenith gear pump obtained fromParker Hannifin Corp., Sanford, N.C.) was used to feed 0.66 kg/h ofheated Escorez™2520 oil (25° C.) into zone 7. Encapsulated microsphereshaving a shell composition containing acrylonitrile andmethacrylonitrile (F100D available from Pierce-Stevens Inc., Buffalo,N.Y.) were added to zone 8 using a K-tron gravimetric feeder (ModelKCLKT20, Pitman, N.J.) at a feed rate of 0.077 kg/h. The screw, havingmultiple kneading and conveying sections, was run at 275 RPM. Theextruder zones were set with a decreasing temperature profile asfollows: zone 2 & 3 at 160° C., zones 5-7 at 120° C., and zones 8-10 at110° C. The expandable adhesive composition was then fed into a 5cm³/rev Zenith gear pump at the exit of the 25 mm extruder andtransported to a Cloeren three layer feedblock (Model 96-1501, Orange,Tex.) using a 1.27 cm OD stainless steel transfer piping that wasoperated at 149° C., and then through a 25.4 cm wide die (Ultraflex 40obtained from EDI Chippewa Falls, Wis.) operated at 177° C. with a diegap of 1.52 mm (60 mils). The extruded material leaving the die was inthe form of a foamed adhesive sheet. The sheet was cast onto a chillroll that was set at 10° C., cooled to about 250° C., and thentransferred onto a 0.127 mm thick polyethylene release liner. Thethickness of the foamed sheet, which was controlled by the collectingweb speed, for Example 38 was 0.5 mm. After cooling, the foam sheet wascovered with another 0.127 mm thick polyethylene release liner andcrosslinked using an electron beam processing unit (Electrocurtain CB300) operating at an accelerating voltage of 300 kV and a measured doseof 6 megaRads (Mrads). The sheet was exposed to the electron beam fromeach of the two major surfaces. The resulting foamed adhesive sheet wastacky. Example 39 was prepared following the procedure for Example 38except the thickness was 1 mm (40 mil).

The foamed adhesive sheets were tested for 90° peel adhesion and staticshear strength. Test results are shown in Table 8.

EXAMPLES 40-49

A pressure-sensitive adhesive foam sheet was prepared following theprocedure for Example 39, except that the 3 layer feedblock was also fedwith molten Hot Melt Composition B such that Composition B wasco-extruded as skin layers on each major surface of the foam sheet.Composition B was melted in a 5.08 cm Bonnot single screw extruder(Model 2″ WPKR, Green, Ohio) with a 5 cm³/rev Zenith gear pump andtransported to the feedblock using a 1.27 cm OD heated stainless steeltransfer piping. The single screw extruder, gear pump, and piping wereoperated at 177° C. The skin layers and the layer containing themicrospheres were combined in the feedblock and then passed through thesingle layer die where it exited as a foamed sheet having adhesive skinlayers. The sheet was collected in the manner described above.

Examples 40-46 were coextruded polymodal asymmetric elastomeric blockcopolymer adhesive foam tapes made with polymodal asymmetric elastomericblock copolymer adhesive skins. The thickness of each of the skin layersof Hot Melt Composition B was 75 micrometers (3 mil) for Example 40 and125 micrometers (5 mil) for Examples 41. Example 42 was preparedaccording to the procedure for Example 41 except that the microspherefeed rate was 0.154 kg/h in zone 8 of the extruder. Example 43 wasprepared according to the procedure for Example 41 except that themicrosphere feed rate was 0.231 kg/h in zone 8 of the extruder. Example44 was prepared according to the procedure for Example 41 except thatthe co-extruded skins were made from Hot Melt Composition A. Example 45was prepared according to the procedure for Example 41 except that theco-extruded skins were made from Hot Melt Composition C. Example 46 wasprepared following the procedure for Example 41 except that theco-extruded skins were Hot Melt Composition C and the feed rates ofcomponents varied as follows. The dry blended mixture of 64 parts ofcopolymer, 36 parts Regalite™S101 tackifier, 1.28 parts Irganox™1010,and 1.28 parts Tinuvin™328, was fed into zone 1 at feed rate of 2.422kg/h; the grid melter fed 1.819 kg/h of molten Regalite™S101 into zone3, and the Zenith gear pump fed 0.295 kg/h of Escorez™2520 oil into zone7 of the extruder. The expandable microspheres were added to zone 8 at0.077 kg/h.

Example 47 was prepared following the procedure for Example 44 exceptthe three feeds to zones 1, 3, and 7 were replaced by a single feed ofHot Melt Composition D into zone 1 of the twin screw extruder from a5.08 cm Bonnot single screw extruder (Model 2″WPKR, Green, Ohio)operated at a flow rate of 4.54 kg/h and temperatures of 175° C. Thepackages of adhesive (Hot Melt Composition D), including the packagingmaterial, had been softened and mixed in the single screw extruder. TheF100D expandable microspheres were added at a feed rate of 0.091 kg/h tozone 8 of the extruder and the co-extruded skins were Hot MeltComposition C. After extrusion, the foams were electron beam crosslinkedusing with a dose of 6 MRad at an accelerating voltage of 300 kV fromboth sides of the foam. Example 48 was prepared following the procedurefor Example 47 except the feed in zone 1 was replaced with Hot MeltComposition E.

Example 49 was prepared by laminating a 50 micrometer thick acrylicpressure-sensitive adhesive transfer tape (9471 LE available from 3MCompany, St Paul, Minn.) to each side of the foam of Example 2 usingfour passes of a 2 kg (4.5 lb) hard rubber roller. These exemplaryadhesives and tapes were tested for 90° peel adhesion and static shearstrength. Test results are shown in Table 8.

TABLE 8 90° Peel Adhesion 90° Peel Adhesion Static Shear - N/dm 3D-RTN/dm 3D-70° min Ex SS PP PE SS PP PE RT 70 38 56 86 44  49  58  40 1000010000 39 156 268 89 159 172  93 10000 10000 40 292 408 208 312 475 21210000 10000 41 343 454 215 326 503 235 10000 10000 42 334 452 187 322503 200 10000 10000 43 208 231 91 270 158 110 10000 10000 44 293 466 135308 434 147 10000 2846 P 45 473 567 138 403 503 219 10000 5848 P 46 545615 159 536 623 254 10000 1934 P 47 487 457 172 508 499 212  173 C  194C 48 384 426 177 308 406 217 3201 C  855 C 49 131 163 42 NT NT NT   88*   3* NT—Not tested *Failed at the adhesive skin/foam interface (i.e.,delaminated)

EXAMPLES 50-53

Hot Melt Composition F was compounded in a 51 mm single screw extruder(Bonnot) for Example 50. The temperatures in the extruder and theflexible hose at the exit end of the extruder were all set at 93.3° C.and the flow rate was controlled with a Zenith gear pump. The compoundedadhesive was then fed to a 30 mm co-rotating twin screw extruder withthree additive ports (Werner Pfleider) operating at a screw speed of 200rpm with a flow rate of about 15 pounds/hour (6.8 kilograms/hour). Thetemperature for all of the zones in the twin screw extruder was set93.3° C. Expandable polymeric microspheres having a shell compositioncontaining acrylonitrile and methacrylonitrile (F80 SD available fromPierce Stevens, Buffalo, N.Y.) were added downstream to the third feedport about three-fourths of the way down the extruder barrel at a feedrate of 1.4 parts by weight per one hundred parts of hot meltcomposition. The hose and die temperatures were set at 193.3° C. Thefoamed extrudate containing the microspheres was pumped to a 3-layerco-extrusion feedblock as the center layer of a 3-layer construction.The feedblock temperature was set at 160° C. Hot Melt Composition C wasfed to a second 51 mm single screw extruder (Bonnot) and compounded. Thetemperatures in the extruder and the flexible hose at the exit end ofthe extruder were all set at 150° C. and the flow rate from wascontrolled with a Zenith gear pump. The compounded composition was thenfed to the feedblock, which split the incoming stream to provide a layerof Hot Melt Composition to each face of the foamed sheet which was thenfed through a 20.32 cm wide drop die shimmed to a thickness of 1.016 mm.The die temperature was set at 182° C. The gear pump was set to provide76 micrometer thick layers of adhesive to each face of the foamed sheet.The resulting foam acrylic sheet having adhesive outerlayers had athickness of about 1145 micrometers. The extruded sheet was cast onto achill roll that was set at 7.2° C., cooled to about 25° C., and thentransferred onto a 0.127 mm thick polyethylene release liner. The sheetswere then cross-linked by exposing to electron beam radiation at ameasured dose of 6 Mrads and an accelerating voltage of 300 kV from bothsides.

Example 51 was prepared following the procedure for Example 50 exceptthat Hot Melt Composition H was used as the foam layer and Hot MeltComposition K as the adhesive skin layers. Example 52 was preparedfollowing the procedure for Example 50 except that Hot Melt CompositionH was used as the foam layer and Hot Melt Composition I as the adhesiveskin layers. Example 53 was prepared following the procedure for Example50 except that Hot Melt Composition H was used as the foam layer and HotMelt Composition A as the adhesive skin layers.

All of these foam tapes were tacky and were tested for peel adhesion andstatic shear. Test results are shown in Table 9.

EXAMPLES 54-59

A commercially available polyethylene foam (0.16 cm thick 6E Foamavailable from Voltek) was primed with Scotch-mount 4298 AdhesionPromotor (available from 3M Company) by applying a thin layer of primerto each side of the foam with a sponge applicator and allowing thesolvent to evaporate (approximately 1 minute). Then the transfer tapeswere laminated to each side of the polyethylene foam using handpressure. Examples 57-59 were prepared in the same manner except thatthe foam was 545 Polyurethane Foam (available from Norton).

The transfer tapes used were: Examples 54 and 57—tape from Example 7except the e-beam conditions were 175 kV at 8 Mrad; Examples 55 and58—tape from Example 14 Examples 56 and 59—tape from Example 28.

Testing results for the laminated tapes are shown in Table 9.

TABLE 9 90° Peel Adhesion - N/dm 5D- Static 100/ T-peel Shear* 1H-RT3D-RT 7D-70° C. 100 N/dm 70° C. Ex Paint PP Paint PP Paint PP PaintPaint Min 50 238 NT 525 NT 536 NT 501 287 10,000 51 109 NT 235 NT 501 NT364 273 10,000 52  77 NT 508 NT 462 NT 476 270 10,000 53 102 NT 469 NT466 NT 312 210 10,000 54 424 NT 347 424 378 399 NT NT NT 55 116 876 175133 399 392 NT NT NT 56 284 193 403 413 406 378 NT NT NT 57 249 154 298308 371 550 NT NT NT 58 245 182 312 308 501 438 NT NT NT 59 182 126 228308 361 336 NT NT NT 60 144 NT 287 NT 549 NT 445 NT 10,000 NT—Not tested*Tested with a 750 g weight and the overlap was 2.54 cm by 2.54 cm

EXAMPLE 60

Example 60 was prepared following the procedure of Example 50 with theexceptions: Hot Melt Composition J was used in the foam layer at a rateof 6.3 Kg/hr. Also, Escorez™ 180 was added to the foam layer via Zenithpump and a heated hose (150 C) and a rate of 7.5 parts per hundred byweight of Hot Melt Composition J. The F80 SD expandable polymericmicrospheres were added at 1.0 part per hundred by weight of the totalpolymer in the foam layer. Hot Melt Composition K was coated on eachmajor surface of the foam layer and was used as adhesive skin layers.

Variations and modifications are possible from the foregoing disclosurewithout departing from either the spirit or scope of the presentinvention as defined in the claims.

1. A pressure sensitive adhesive article comprising: a backing havingfirst and second major surfaces; and a pressure sensitive adhesive on atleast a portion of at least one of the major surfaces of said backing,at least one of said backing and said adhesive has a rubber phase andcomprises: (a) 100 parts by weight of a polymodal asymmetric elastomericblock copolymer; (b) at least one tackifier in an amount sufficient toraise the calculated Fox T_(g) of the rubber phase of said adhesive toat least 245°K; (c) 0 to about 50 parts by weight of a crosslinkingagent; and (d) 0 to about 300 parts by weight of a plasticizer; whereinsaid polymodal asymmetric elastomeric block copolymer has the formulaQ_(n) Y and comprises from about 4 to about 40 percent by weight of apolymerized monovinyl aromatic compound and from about 96 to about 60percent by weight of polymerized conjugated diene, wherein: Q representsan individual arm of said block copolymer and has the formula S-B; nrepresents the number of arms Q in said block copolymer and is a wholenumber of at least 3; and Y is the residue of a multifunctional couplingagent; and further wherein: (a) S is a nonelastomeric polymer segmentendblock of a polymerized monovinyl aromatic homopolymer, there being atleast two different molecular weight endblocks in said copolymer, ahigher molecular weight endblock and a lower molecular weight endblock,wherein: (i) the number average molecular weight of said highermolecular weight endblock (Mn)_(H) is in the range of from about 5,000to about 50,000; (ii) the number average molecular weight of said lowermolecular weight endblock (Mn)_(L) is in the range of from about 1,000to about 10,000; and (iii) the ratio (Mn)_(H)/(Mn)_(L) is at least 1.25;and (b) B is an elastomeric polymer segment midblock which connects eacharm to the residue of a multifunctional coupling agent (Y) and comprisesa polymerized conjugated diene or combination of conjugated dienes,wherein when said adhesive comprises said block copolymer, wherein saidadhesive comprises a foam having at least one substantially smooth majorsurface having an Ra value less than about 75 micrometers, as measuredby laser triangulation profilometry, and said foam comprises a pluralityof microspheres, at least one of which is an at least partially expandedexpandable polymeric microsphere.
 2. The pressure sensitive adhesivearticle according to claim 1, wherein said at least one tackifier is inan amount sufficient to raise the calculated Fox T_(g) of the rubberphase of at least one of said adhesive and said backing to at least250°K.
 3. The pressure sensitive adhesive article according to claim 1,wherein said adhesive exhibits a 180° peel strength on an HDPE substrateof at least 60 N/dm.
 4. The pressure sensitive adhesive articleaccording to claim 1, wherein said tackifier is a low acidic or neutraltackifier.
 5. The pressure sensitive adhesive article according to claim1, wherein said tackifier has a T_(g) in the range of from about −50° C.to about 200° C.
 6. The pressure sensitive adhesive article according toclaim 1, wherein said tackifier has a softening point of above 80° C. 7.The pressure sensitive adhesive article according to claim 1, whereinthe polymodal asymmetric elastomeric block copolymer is crosslinked. 8.A pressure sensitive adhesive having a rubber phase, said adhesive beingin the form of a foam having at least one substantially smooth majorsurface having an Ra value less than about 75 micrometers, as measuredby laser triangulation profilometry, said foam comprising a plurality ofat least partially expanded expandable polymeric microspheres, and atleast one other polymer composition in the form of a plurality ofdiscrete structures being bonded to or embedded in said foam, and saidadhesive comprising: (a) 100 parts by weight of a polymodal asymmetricelastomeric block copolymer; (b) at least one tackifier in an amountsufficient to raise the calculated Fox T_(g) of the rubber phase of saidadhesive to at least 245°K; (c) 0 to about 50 parts by weight of acrosslinking agent; and (d) 0 to about 300 parts by weight of aplasticizer; wherein said polymodal asymmetric elastomeric blockcopolymer has the formula Q_(n) Y and comprises from about 4 to about 40percent by weight of a polymerized monovinyl aromatic compound and fromabout 96 to about 60 percent by weight of polymerized conjugated diene,wherein: Q represents an individual arm of said block copolymer and hasthe formula S-B; n represents the number of arms Q in said blockcopolymer and is a whole number of at least 3; and Y is the residue of amultifunctional coupling agent; and further wherein: (a) S is anonelastomeric polymer segment endblock of a polymerized monovinylaromatic homopolymer, there being at least two different molecularweight endblocks in said copolymer, a higher molecular weight endblockand a lower molecular weight endblock, wherein: (i) the number averagemolecular weight of said higher molecular weight endblock (Mn)_(H) is inthe range of from about 5,000 to about 50,000; (ii) the number averagemolecular weight of said lower molecular weight endblock (Mn)_(L) is inthe range of from about 1,000 to about 10,000; and (iii) the ratio(Mn)_(H)/(Mn)_(L) is at least 1.25; and (b) B is an elastomeric polymersegment midblock which connects each arm to the residue of amultifunctional coupling agent (Y) and comprises a polymerizedconjugated diene or combination of conjugated dienes.
 9. The pressuresensitive adhesive article according to claim 1, further comprising asecond adhesive layer on said first or second major surface of saidbacking.
 10. The pressure sensitive adhesive article according to claim9, wherein said second adhesive layer comprises an adhesive compositionthat differs from said pressure sensitive adhesive.
 11. The pressuresensitive adhesive according to claim 8, further comprising at least oneadditional layer on an outer surface of said foam, said at least onelayer comprising a foam polymeric layer, a non-foamed polymeric layer,an expandable microsphere-containing layer, a wood substrate, a metallayer, or a release liner.
 12. The pressure sensitive adhesive articleaccording to claim 1, wherein said backing comprises a foam backing. 13.The pressure sensitive adhesive article according to claim 12, whereinsaid backing comprises said block copolymer, and said adhesive comprisesa blend of two or more polymers.
 14. A pressure sensitive adhesivearticle comprising: a backing having first and second major surfaces;and a pressure sensitive adhesive on at least a portion of at least oneof the major surfaces of said backing, at least one of said backing andsaid adhesive has a rubber phase and comprises: (a) 100 parts by weightof a polymodal asymmetric elastomeric block copolymer; (b) at least onetackifier in an amount sufficient to raise the calculated Fox T_(g) ofthe rubber phase of said adhesive to at least 245°K; (c) 0 to about 50parts by weight of a crossliniking agent; and (d) 0 to about 300 partsby weight of a plasticizer; wherein said polymodal asymmetricelastomeric block copolymer has the formula Q_(n)Y and comprises fromabout 4 to about 40 percent by weight of a polymerized monovinylaromatic compound and from about 96 to about 60 percent by weight ofpolymerized conjugated diene, wherein: Q represents an individual arm ofsaid block copolymer and has the formula S-B; n represents the number ofarms Q in said block copolymer and is a whole number of at least 3 and Yis the residue of a multifunctional coupling agent; and further wherein:(a) S is a nonelastomeric polymer segment endblock of a polymerizedmonovinyl aromatic homopolymer, there being at least two differentmolecular weight endblocks in said copolymer, a higher molecular weightendblock and a lower molecular weight endblock, wherein: (i) the numberaverage molecular weight of said higher molecular weight endblock(Mn)_(H) is in the range of from about 5,000 to about 50,000; (ii) thenumber average molecular weight of said lower molecular weight endblock(Mn)_(L) is in the range of from about 1,000 to about 10,000; and (iii)the ratio (Mn)_(H)/(Mn)_(L) is at least 1.25; and (b) B is anelastomeric polymer segment midblock which connects each arm to theresidue of a multifunctional coupling agent (Y) and comprises apolymerized conjugated diene or combination of conjugated dienes,wherein when said adhesive comprises said block copolymer, said adhesivefurther comprises (i) a plurality of unexpanded expandable microspheres,(ii) a plurality of at least partially expanded expandable microspheres,or (iii) a combination of (i) and (ii), and said backing comprises afoam backing.
 15. The pressure sensitive adhesive article according toclaim 14, wherein said backing comprises said block copolymer, and saidadhesive comprises a blend of two or more polymers.
 16. The pressuresensitive adhesive article according to claim 14, wherein said at leastone tackifier is in an amount sufficient to raise the calculated FoxT_(g) of the rubber phase of at least one of said adhesive and saidbacking to at least 250°K.